Thе plaintiff and the defendant entered into three separate advertising contracts. The defendant is an advertising agent who operates under the name Ad Infinitum from his home. All negotiations relative to these contracts were conducted between the defendant and William Rasmussen, a former emрloyee of the plaintiff. The contracts called for the plaintiff to provide advertising services for a Grinold Auto Parts, Inc.
The first contract, datеd February 6, 1976, was for a one eighth sponsorship in ten games in the plaintiffs radio broadcasts for the 1975-1976 hockey season. The second contract, dаted February 9,1976, was for advertising in the Whalers Blue Line Magazine for the 1975-1976 season. The third contract, executed in early April of 1976, was for a one eighth sponsorship in the plaintiff’s radio broadcasts for the 1975-1976 season playoffs. The plaintiff fulfilled its obligations under the contracts but was not paid for its services.
Thе three contracts named “Grinold Auto Parts, Inc.,” as the client and each was signed by the defendant. On the first and third contracts, the defendant signed the documеnt over the word “Officer.” On the second contract, the defendant signed the document on the line marked “authorized by,” and the initials “V.P.” were placed next to his name over the word “title.” The defendant’s home address was used on the *682 contracts. All bills were sent to the defendant at his home address within a short pеriod after each ad appeared or was broadcast.
This is an action on a debt in which the plaintiff seeks to recover for its advertising sеrvices provided to the defendant. The defendant, by way of a special defense, alleged that he was not a principal party to the thrеe contracts, but acted as an advertising agent for Grinold Auto Parts, Inc. The trial court found that the defendant was not an agent of Grinold Auto Parts, Inc., but that he acted as a principal to the contract and, thereby, was personally liable to the plaintiff. Judgment was rendered for the plaintiff in the amount of $7437.50 plus interest from June 18, 1979, the date on which the plaintiff filed an offer of judgment. The defendant appeals. 1
The defendant assigns as errors 2 essentially (1) that the trial court erred in ruling that the defendant acted as a principal in contracting with the plaintiff; (2) that the trial court erred in ruling that the advertiser, “Grinold Auto Parts, Inc.,” was a trade namе and not a Connecticut corporation; (3) that the trial court erred in failing to draw an unfavorable inference under the Secondino rule from the plaintiff’s failurе to call William Rasmussen as a witness on its behalf; and (4) that if the trial court’s judgment is correct, there is error in awarding the plaintiff interest from the time the plaintiff filed an offer of judgment.
*683 I
The defendant’s claim of error that the trial court erred in finding him individually responsible for the debt is without merit. To avoid personal liability, it is the duty оf an agent to disclose both the fact that he is acting in a representative capacity and the identity of his principal, since the party with whоm he deals is not required to discover or to make inquiries to discover these facts.
Klepp Wood Flooring Corporation
v.
Butterfield,
The existence of an agency relationship is a question of fact for the trier.
Botticello
v.
Stefanovicz,
On the basis of the evidence, the trial court reasonably determined that the defendant did not act as an agent. It is the function of the trial court to weigh the evidence and judge the credibility of the witnesses.
Murphy
v.
Dell Corporation,
II
The defendant’s second claim of error is equally without merit. At the time the contracts were executed, Grinold Auto Parts, Inc., was not the legal name of any corporation in Connеcticut. The certificate of authority showed that since March 17, 1965, the owner of these auto supply stores had been R.W. Grinold Realty Company, Inc. During thе trial, the defendant offered no plausible explanation as to why he supplied the plaintiff with the name Grinold Auto Parts, Inc., one of the several names under which R.W. Grinold Realty Company, Inc., was doing business. The agent’s use of a trade name under which the principal transacts his business is not a sufficient identification of the principal *685 to protect the agent from personal liability. 3 C. J.S., Agency § 371. We hold that the trial court’s finding is not clearly erroneous.
III
The advеrse inference rule is defined as the failure of a party to produce a witness who is within his power to produce and who would naturally have beеn produced by him which failure permits the inference that the evidence of the witness would be unfavorable to the party’s cause.
State
v.
Kish,
IV
The defendant’s final claim challenges the propriety of the interest award from the time the plaintiff filed an offer of judgment. Our Supreme Court has reсently addressed this issue and held, in
Gionfriddo
v.
Avis
*686
Rent A Car System, Inc.,
There is no error.
In this opinion the other judges concurred.
Notes
This appeal was originally filed in the Appellate Session of the Superior Court. Public Acts, Spec. Sess., June, 1983, No. 83-29, § 3 (c).
The defendant has raised five additional issues in his statement of issues. The defendant, hоwever, has not properly briefed any of them. Since counsel has not researched the issues or formulated any legal arguments thereunder, we deem the issues to be abandoned.
Sturman
v.
Socha,
At this time the defendant’s account with the plaintiff was past due. In forebearance of the defendant’s statement that he would pay the outstanding amount, the plaintiff did not send the matter to its attorney for collection.
