I've recently (past 2 months) had excellent experiences. Initially my aprehensions were similar to yours. The good ones are easy to spot if you follow their threads and comments. Just look up their profile and browse the history of participation. As mentioned above, look at the feedback from the seller. It will save you a lot of headaches. If by chance they don't have any feedback, send them a question and see what the response is. On the most part, 98%, the members are the real deal. You have to filter out the ones who are not, but then, the other members will probably call them out before they get a chance to do much damage.
As it relates to Paypal. If something goes wrong you have recourse, which means if you document the process in a reasonable fashion you can get your money back.
So, good luck. Give it a shot. It's a wonderful forum.