The short answer is to know the guns well enough that you don't have to rely on dealer reputations to make decisions about whether a pistol is original and correct or not.

While a seller's customer service record may be important to some, the key is to buy a good gun in the first place. Ask questions and request enough and proper photos if buying online or mail order. The responsibility and the consequences of any purchase ultimately lie with the purchaser.

I find dealer feedback ratings are useless for the most part with some sellers. Just because a buyer is happy with his purchase does not speak to how knowledgeable he is, or to how original or correct the pistol is. Great customer service and honesty is not a substitution for originality.

I typically try to buy face-to-face. That eliminates the question of how reputable the seller is. It does, however, raise the question of how knowedgeable and experienced I am with the pistols I try to collect. that question is answered everytime a knowledgeable collector views something I bought.

Learn first...buy later. Just my opinion.