This is certainly a grey area which is open to all possibilities.
Ethically, the dealer is responsible for nothing as long as he knew nothing about impending problems. The gun did work upon delivery after all.
Of course if the dealer "fixed" the gun with rubber bands and chewing gums before delivery, or knew about flaky operation, then he is at fault for not disclosing anything.
Even if the dealer knew nothing of the problem, and if he would like repeat business from said customer, he probably should share some of the repair costs on a good will basis.
To some extent, the fact that the gun is a stock item or a consignment makes a difference. Expect less from a consignment situation.
Some dealers are great for service, some others not so much...
Some are plain incompetent...Some are fair price wise, some are atrociously overpriced. It's all over the map...
Best regards,
WC-