I have used Game Gavel as a selling platform for a few years and have had success with it. I've had 250+ transactions. I think because so few people used it, my listing really stood out. I was the only seller selling imports. I made a little storefront page and I would just link people from my facebook or twitter. I don't think many people just stumbled upon GG but I could point them toward it. And I had no fees other than paypal, which was my reason to use it over ebay.
On the negative side, GG could be fickle and it was often down or buggy. Sometimes several weeks would pass when it was down and I couldn't even log in to check my sales. I am looking forward to seeing what the new owner does with the site. From my point of view, I wold be happy if they just kept the existing site bug free. I hope that the redesign is not so drastic that I have to relist everything from scratch.
I know a lot of people had no luck with GG in the past, and I don't mean to downplay anyone else's experiences, but just saying it worked out well for me and I remain cautiously optimistic that it will continue to do so.