I agree with most of the points made. I have bought my guns between my local shop, GB and the S&W sites. I picked up my first presentation box, brushes, screwdriver and 8" Model 27-2 for about $600 (at my local shop), I considered it fair because I could afford it, I did not have one and it came along at the RIGHT TIME! I have got most of my long guns on GB. My DA Ruger & most of my S&W's came from the S&W site. Most S&W's on GB are irrationally priced. I, for example, can't afford the new S&W's, so that's why I search the used sites. I am not a fanatic about the new lock system that most S&W people hate, I'm just trying to get stuff I can afford.
Again it's what you are looking for and what is available and where it is and where you are. Being from NJ I have to plan my purchases around permits which can be 3-6 months ahead of time. If I lived in Virginia or somewhere else, I would plunk my money and my Driver's license on the counter and walk out.
The other big problem with all auction sites (not just gun related ones), is when I hear/read the seller say "I need this much to buy something else...". Once I see that, then I know fair pricing is out the window. Because this clown wants to buy something he can't afford, so he is trying to put a higher value on a lesser item of his to get what he wants.
As an aside to all our Baseball fans who will understand, it is the same thing with trades. Most fans of a team think their junk is great and greatly desired by everyone else. For example, I am a Cardinal fan. I am sure there are some Met fans out there who think that 3 minor league prospects in their farm system would be a great trade for a Carpenter or a Wainwright. I would respectfully reply, "Are you serious"? But again that is human nature, to value your stuff while de-valuing others, right?