I'm a collector and have never sold a gun on a website; so can only speak from the/my collector's perspective. I've purchased guns from GB, GI, and GA; and I've done so because each has, from time to time, listed a specific item/s I wanted. And I've also passed on a lot more items posted to these sites because I thought they were overpriced or out of my budget. I personally don't like the 15 minute rule on GB, but have purchased more guns thru GB than any of the other auction sites. I suppose that's because their size provides more opportunities, but many times I was the only bidder on the weird guns I appreciate and got a bargain; and am convinced that poor descriptions and poor photos furnished by the seller was responsible for the lack of bidding. I've purchased the fewest number of guns thru the GA web site than the other two; but check it regularly because one never knows where an unusual Syracuse, Hollenbeck, or Baltimore might pop up. The main thing I appreciate about GI and GA is knowing the sellers asking price up front as I know immediately if I can be a player or not. Sometimes a seller is negotiable on his asking and sometimes not; but if I see the gun as being reasonably priced, then I'm OK with a non-negotiable price.
