Not only reputable dealers, but just regular guys here do things right. Recently I received a rifle from a member here that, in my opinion, was not what I had paid for. I contacted the vendor immediately. Neither of us were pleased with the situation. Nobody likes a deal to go sideways. We worked it out, both of us learned something from the experience, and I would deal with him again in a heartbeat.
I have never had a firearm returned, but several years ago a member was not happy with a scope mount I sent him. Easy, just send it back for a full refund.
The fly in the ointment in original posters situation is the five month time lapse before notifying the vendor. Having said that, I would think that the vendor would consider some adjustment if he were approached properly, and not beat up on the net.
Ted