Generally speaking, there are two types of auctions: estate–type auctions and consignment auctions.
In estate–type auctions, the articles to be auctioned (including firearms) are being sold by the executor of the estate of an individual. The firearms belong to and are possessed by the executor. The firearms are controlled by the estate, and the sales of firearms are being made by the estate. The auctioneer is acting as an agent of the executor and assisting the executor in finding buyers for the firearms. In these cases, the auctioneer does not meet the definition of engaging in business as a dealer in firearms and would not need a license. An auctioneer who does have a license may perform this function away from his or her licensed premises.
In consignment–type auctions, an auctioneer often takes possession of firearms in advance of the auction. These firearms are generally inventoried, evaluated, and tagged for identification. The firearms belong to individuals who have entered into a consignment agreement with the auctioneer giving that auctioneer authority to sell the firearms. The auctioneer therefore has possession and control of the firearms. Under these circumstances, an auctioneer would generally need a license. If you are not sure if a license is needed in a particular consignment auction situation, contact your local ATF office.