I bought and sold some on Gunbroker. But got taken advantage of by a seller on there along with several other people.
Forget about collecting anything from their "insurance" They did nothing to help.
I had to do all the leg work and if it hadn't been for the seller scamming multiple thousands of dollars enough to really tick people off I did get my money back from the seller but nothing from Gunbroker just run around.
They are ok but make sure who you are buying from. I haven't used them since I switched to Auction Arms
http://www.auctionarms.com/
I have had many good transactions on gunbroker but when in mattered they were of no help