OPINION
¶ 1 Arizona Revised Statute (“A.R.S.”) section 11-254.01(A) (2001) requires counties to procure contractual services over a specified dollar value, other than professional services, by sealed, competitive bids. To decide the appeal in this legal malpractice case, we must delineate the “professional services” that are exempt from the competitive bid requirement. After resolving that issue and others, we affirm the trial court’s judgment.
FACTS AND PROCEDURAL HISTORY
¶ 2 On July 15, 1996, La Paz County and appellant Western Corrections Group, Inc. (“WCG”) entered in a “Project Expediter Agreement” (“Agreement”), whereby WCG agreed to assist the County Supervisors and serve as their agent “in planning, designing, contracting, implementing and constructing” two County facilities and “by selecting and expediting the work of an architect and/or engineer and contractor for the Project.” The County did not submit the Agreement for competitive bid. WCG is operated by Wesley Box, who signed the Agreement as WCG’s authorized agent. Neither WCG nor Box was licensed as a contractor, engineer, or architect.
¶ 3 The Agreement segregated WCG’s duties into three stages: planning, bidding, and construction. WCG was required to pay all costs, fees, and expenses incurred in performing its duties. In return for WCG’s services, the County agreed to compensate WCG by paying it 13% of the total construction costs for the facilities, which the County would pay pursuant to a payment schedule set forth in the Agreement. The schedule also required the County to pay WCG $1,000 upon execution of the Agreement, which the County paid on July 15,1996.
¶ 4 During the planning stage of the project, WCG procured architectural plans and specifications to be used in a project bid package and submitted them to the County. The County Board of Supervisors subsequently accepted the bid package and authorized payment of $360,000 to WCG pursuant to the terms of the payment schedule. Consequently, on November 12,1996, the County issued WCG a $360,000 warrant for payment. On November 21, however, the county treasurer refused to honor the warrant. Thereafter, WCG hired appellee David Tierney and Sacks Tierney, P.A. (collectively, “Tierney”), to represent it in an attempt to collect on the warrant.
¶ 5 On December 24, Tierney filed a complaint in federal district court for mandamus relief against the county treasurer, seeking to compel payment of the $360,000 warrant. The district court later dismissed the complaint for failure to join the County as an indispensable party.
¶ 6 On September 2, 1997, a newly elected Board of Supervisors, which questioned the legality of the Agreement, voted to cancel the Agreement and rescind the warrant. Thereafter, the County returned the plans and specifications to WCG, the facilities were never built, and no construction costs were incurred.
¶ 7 On May 13, 1998, Tierney sent a notice of claim to the County pursuant to A.R.S. § 12-821.01 (2003), which requires a person with a claim against a public entity or a public employee to provide notice of that claim within 180 days of the date the claim accrued. Failure to comply with this provision bars any claim. Id. at § 12-821.01(A).
¶ 8 On September 9, the County filed a complaint in superior court seeking a declaration of the parties’ rights under the Agreement. WCG counterclaimed for breach of contract and quantum meruit. The court eventually dismissed WCG’s counterclaim because WCG, through Tierney, had failed to timely file a notice of claim as required by A.R.S. § 12-821.01(A). As a result, WCG sued Tierney for professional negligence (legal malpractice), breach of fiduciary duty, and fraud, and sought both compensatory and punitive damages.
¶ 9 The trial court granted partial summary judgment in favor of Tierney. The court ruled that WCG would have lost its *586 case against the County because the Agreement was unenforceable due to the County’s failure to comply with applicable statutory provisions, and WCG was not otherwise entitled to receive compensation from the County. Consequently, the court determined that WCG could not recover any damages for legal malpractice based on its contention that it would have prevailed against the County but for Tierney’s failure to timely submit the notice of claim. The court further found that the evidence did not support a punitive damages award. After the court’s ruling, the claims remaining for trial concerned only whether WCG was entitled to recover attorneys’ fees and costs expended to pursue its claim against the County after expiration of the 180-day time limit to file a notice of claim.
¶ 10 Prior to trial, Tierney voluntarily paid $83,709.28 to WCG, representing attorneys’ fees and costs expended by WCG for actions taken after the expiration of the 180-day time limit. A jury subsequently found in favor of WCG on the negligence and fraud claims, but against it on the breach of fiduciary duty claim. The jury assessed damages in the amount of $83,709.28. Upon Tierney’s motion, the court entered judgment as a matter of law in favor of Tierney on the fraud claim. Additionally, the court credited Tierney with the pretrial payment, thereby reducing the damages verdict to zero. After entry of judgment, this appeal followed. 1
DISCUSSION
¶ 11 To prevail on its legal malpractice claim, WCG was required to show that but for Tierney’s failure to timely file a notice of claim, WCG would have been successful in the “case within the case,” which was WCG’s lawsuit against the County.
Hyatt Regency Phoenix Hotel Co. v. Winston & Strawn,
¶ 12 WCG argues that the trial court erred by ruling as a matter of law that WCG would have lost its case against the County because (1) the Agreement was not void due to statutory violations, (2) even if one or more violations occurred, the County was estopped from relying on these provisions to void the Agreement, and (3) alternatively, WCG was entitled to recover damages in quantum meruit. We address each contention in turn.
A. Statutory violations
¶ 13 The trial court ruled that the Agreement was void and thus unenforceable because (1) A.R.S. § 11-254.01(A) required the County to submit the project expediter job for competitive bid, and (2) contrary to the terms of the Agreement, A.R.S. §§ 34-102(A), — 104(A) (2000 & Supp.2003) required the County to directly employ and contract with the project architect and engineer. A public contract entered in violation of a statute is invalid and unenforceable.
Mohave County v. Mohave-Kingman Estates, Inc.,
¶ 14 Section 11-254.01 provides as follows:
A. All purchases of supplies, materials, equipment and contractual services except professional services, made by the county having an estimated cost in excess of ten thousand dollars per transaction ... shall be based on sealed, competitive bids.
D. Professional services shall be procured pursuant to written policies developed by the county purchasing agent and adopted by the board of supervisors.
(Emphasis added.) As with all competitive bid statutes, the purpose of § 11-254.01(A) is to prevent favoritism, fraud and public waste by encouraging free and full competition, and to secure the best work for the lowest, practicable price.
Achen-Gardner, Inc. v. Superior Court,
¶ 15 The County did not submit the project expediter job for competitive bid. WCG argues, however, that competitive bidding was not mandated because a project expediter provides “professional services,” which are exempted under § 11-254.01(A). Tierney, not surprisingly, takes the opposite view. Because the legislature did not define “professional services,” we employ accepted principles of statutory construction to discern the meaning of the term.
¶ 16 The cardinal rule of statutory interpretation is to ascertain the legislature’s intent in adopting the provision.
City of Phoenix v. Superior Court,
¶ 17 To determine the plain meaning of a term, we refer to established and widely used dictionaries.
State v. Wise,
¶ 18 Adoption of these definitions is supported by the limited legislative history for § 11-254.01(A).
Yslava v. Hughes Aircraft Co.,
¶ 19 An interpretation of “professional services” that focuses on specialized education, training, and predominant use of intellectual skills is also consistent with usage of the term in the state procurement code.
State v. Thomason,
¶ 20 Based on the foregoing, we conclude that the term “professional services,” as used in A.R.S. § 11-254.01, refers to those services rendered by a person engaging in a recognized discipline that necessarily requires advanced training and specialized knowledge to perform. Such services also typically result from the predominant use of intellectual skills rather than physical skills. Our interpretation is consistent with those employed by other courts and authorities. 2 Bearing this definition in mind, we now decide whether a project expediter renders “professional services” so as to exempt that job from the bid requirements of § 11— 254.01(A).
¶ 21 In determining whether a service is a professional one, we look at the nature of the involved acts rather than the title afforded the actor.
W.H. Opie,
B. Equitable Estoppel
¶ 22 The trial court rejected WCG’s alternative argument that the County was precluded by principles of equitable estoppel from denying the validity of the Agreement. Specifically, WCG asserted that because the County’s attorney drafted the Agreement, and the board of supervisors approved it, the County was estopped from avoiding the Agreement due to any statutory violations. The court disagreed, ruling that WCG was not entitled to rely on equitable estoppel because the Agreement was illegal and the county facilities were not constructed.
¶ 23 Although a governmental entity is not generally subject to equitable estoppel, the defense can apply under the following circumstances: (1) the government engaged in affirmative conduct inconsistent with a position it later adopted that is adverse to the claimant, (2) the claimant actually and reasonably relied on the government’s prior conduct, (3) the government’s repudiation of its prior conduct caused the claimant to suffer a substantial detriment because it changed its position in a way not compelled by law, and (4) applying estoppel against the government would neither unduly damage the public interest nor substantially and adversely affect the exercise of governmental powers.
Valencia Energy Co. v. Ariz. Dep’t of Revenue,
¶24 Our courts have regularly held that equitable estoppel cannot apply to enforce a contract that is void as against public policy.
Clark v. Tinnin,
¶ 25 As previously stated, ¶ 21 supra, the Agreement between the County and WCG was void because the County failed to submit the project expediter job for public bid, as mandated by A.R.S. § 11-254.01. For this reason alone, equitable estoppel could not be invoked to resurrect the Agreement. See
supra,
¶ 24. Indeed, as the purpose of § 11-254.01 is to prevent favoritism, fraud and public waste,
Achen-Gardner, Inc.,
*590 C. Quantum Meruit
¶ 26 WCG finally contends that the trial court erred by ruling that WCG would not have recovered moneys from the County under a theory of quantum meruit. The court ruled that WCG would not have prevailed on this theory because the County cancelled the Agreement and WCG never completed the work. WCG argues that it was not required to have completed its duties under the Agreement in order to have received the value of its services in hiring an architect and paying that person to draft plans and specifications for the County facilities. Tierney counters that quantum meruit damages are not recoverable on a void public contract or, alternatively, such damages were not available to WCG because the County did not retain the submitted plans and specifications.
¶27 “Quantum meruit” is the measure of damages imposed when a party prevails on the equitable claim of unjust enrichment.
Landi v. Arkules,
¶ 28 We reject Tierney’s contention that quantum meruit damages are never recoverable for performance of a void public contract. Arizona, unlike many jurisdictions, does not impose a blanket prohibition on the recovery of such damages.
Id.; see also Town of Holbrook v. Girand,
¶ 29 We agree with Tierney’s alternative contention that WCG would not have prevailed on its unjust enrichment claim against the County because the County did not retain any benefit bestowed by WCG. WCG argues that it conferred a compensable benefit on the County by providing it with architectural plans and specifications to be used in bid packages for the proposed construction projects. But the County returned the plans and specifications to WCG, can-celled the construction projects, and never built the proposed facilities. Although WCG suggests that the County used the plans and specifications in deciding not to pursue the projects, it does not cite any evidence to that effect. “ ‘Restitutionary relief is allowable only when it would be inequitable or unjust for defendant to
retain
the benefit without compensating plaintiff.’ ”
Creative Learning Sys., Inc. v. State,
¶ 30 WCG mistakenly relies on
Guirey, Srnka & Arnold, Architects v. City of Phoenix,
CONCLUSION
¶ 31 For the foregoing reasons, we hold that the term “professional services,” as used in A.R.S. § 11-254.01, refers to those services rendered by a person engaging in a recognized discipline that necessarily requires advanced training and specialized knowledge to perform. Such services also typically result from the predominant use of intellectual skills rather than physical skills. Applying this definition, we further conclude that WCG did not provide professional services to the County, and the trial court therefore correctly ruled that the Agreement between those parties was void because it was not the product of competitive bidding. We additionally agree with the court that the County was not estopped from contesting the validity of the Agreement, and that WCG was not entitled to recover damages in quantum meruit. Therefore, and for the reasons set forth in our unpublished memorandum decision, we affirm.
Notes
. By separate unpublished decision filed this date, we address additional issues raised on appeal that are not relevant to our analysis in this opinion and do not meet the standards of publication set forth in Arizona Rule of Civil Appellate Procedure 28(b).
Fenn v. Fenn,
. The definition of “professional service” commonly employed in other jurisdictions originated in
Marx v. Hartford Accident & Indem. Co.,
. WCG cites to
Dana, Larson, Roubal & Assoc. v. Bd. of Comm’rs,
