I sell and buy on GB, but have only bought on GI. Gotta pay attention to sellers on both sites. Look at feedback.
I wont bid on NR sellers, no rating, and on my sales listings I also tell buyers with NR to contact me first before bidding.
Worst things happened to me was on a GI buy, a model 70 with a cracked stock. Seller insisted it happened on my end, not possible but I found it with naked eye. Told him I wanted a refund and return of rifle, nope, nada.
GI was no help at all and ended up banning me for being a PITA over it. I reregistered later with a different email. I still buy there but only from sellers with some history.
Had a really rough looking old Mauser show up with deep pitting in the receiver from a GB seller. My FFL guy said it unsafe to shoot, seller wouldnt take it back. I parted it out and sold the parts on GB. I lost a few bucks but here again GB was not much help.
They talk a good guarantee but make you jump through a lot of hoops for it. Too much trouble.
Caveat Emptor....