I've purchased one rifle from GB and one rifle from gunauction.com - didn't have a problem with either transaction. Just to echo what some of the others have already stated, pay attention to sellers with good feedback and use common sense. I don't necessarily rule out sellers with low feedback numbers....they have to start somewhere, but a seller with consistent high feedback will offer me more security with my purchase.
As for not being able to handle a gun, that's the price you pay to use an online auction site. It's important that you know what you're buying before you even place your bid. Do your homework and research the firearm you're interested in, that way, you'll have some idea as to whether or not a seller is full of it or if his item for sale is an honest listing. Communication is also important. Ask the seller questions, lots of questions and be sure to read the terms of the auction very carefully. I've had plenty of non-responses from sellers and I tend to avoid them like the plaque. If they can't take 2 minutes of their time to respond to my question then they're either hiding something or they just don't give a damn.