A violation of this act by an apprentice auctioneer or other employee of a licensed auctioneer shall not be grounds for the revocation or suspension of the license of the sponsor of the apprentice auctioneer or employee unless it appears at the hearing that the sponsor had knowledge of the violation. A course of dealing shown to have been consistently followed by an apprentice auctioneer or employee constitutes prima facie evidence of knowledge upon the part of the sponsor.