My GB experiences have been good.
If I'm looking for a particular firearm and it is available in one of the three shops in the local area I'm comfortable dealing with, I'll buy it there.
If however it's something they don't have, I'll certainly start watching Gun Broker and Guns America to find it.
I am picky about sellers and methods of payment however. If the only method of payment they accept is a money order, I won't bother bidding. Money orders protect the seller, but the post office won't even begin to investigate for at least 6 weeks, then all they will do is confirm whether the seller got the payment o which you already know if you sent it registered mail with a receipt requested.
I am however more than happy to pay 3.5% to cover a credit card fee as it gives me 60 days of protection in the event the firearm never arrives, or is not anywhere close to being as described by the seller.
I do think from time to time some bidders don't think the total costs through in terms of transfer fee, shipping, and in some cases sales tax when they set their maximum bid and if they don't do that, they run the risk pf paying too much.
My biggest annoyance with GB are the sellers who keep listing a firearm with an excessively high buy it now price or an excessively high reserve price - over and over again. They just plug up the search engine and make it harder to find sellers serious about selling. If I see a firearm with a reserve, a completed auction search will normally identify whether it's one of "those" listings.