Trader rating gives you an idea
It is always a risk of sending money to someone and hoping that they'll send you the item(s) in the condition they are supposed to be in. I always stick to going to someone and paying them in cash, that way you can look at the item before paying. Of course it's impossible to do that if they're not close by, so then you just have to trust them. Thankfully most people on here and other enthusiasts sites are trustworthy.
But yeah as for a buyer protection system, what would you do? Make everyone pay through paypal?