I'll name 3 dealers that either paid for repair or promptly refunded my money for used guns that had hidden issues or developed malfunctions shortly after purchase:

Jaqua's, Steve Cobb, Cabela's.

They didn't have to take care of me but they did & I still do business with all of them & I recommend them to others. It's simply smart business to operate this way.

That said, in buying used guns I normally ask for a 3 day shooting inspection & I usually get agreement on this.