The most important thing for sites like this is the feedback system. Most sites such as eBay (And others like it) have a feedback system of some sorts in place so you can tell the good sellers who will ship a good product on time, from the bad sellers who will either be late or take the money and not send it at all.
Other than that it's pretty much a blind leap of faith when dealing with these types of transactions, you just have to hope for the best. Hopefully this helped a little.
Other than that it's pretty much a blind leap of faith when dealing with these types of transactions, you just have to hope for the best. Hopefully this helped a little.