5 C.F.R. § 2635.201
(b) Considerations for declining otherwise permissible gifts.
(2) Employees who are considering whether acceptance of a gift would lead a reasonable person with knowledge of the relevant facts to question their integrity or impartiality may consider, among other relevant factors, whether:
(4) Employees who have questions regarding this subpart, including whether the employee should decline a gift that would otherwise be permitted under an exception found in § 2635.204, should seek advice from an agency ethics official.
Example 1 to paragraph (b): An employee of the Peace Corps is in charge of making routine purchases of office supplies. After a promotional presentation to highlight several new products, a vendor offers to buy the employee lunch, which costs less than $20. The employee is concerned that a reasonable person may question their impartiality by accepting the free lunch, as the timing of the offer indicates that the donor may be seeking to influence an official action and the company has interests that may be substantially affected by the performance or nonperformance of the employee's duties. The employee concludes that appearance considerations weigh against accepting the gift.