It's just the same with any community, online or not. Not to mention eBay.
Although I consider this much better than eBay because we have what they don't - actual interaction with people within the community. Feedback only tells you so much. But here...it's like a family. You get to know people on a personal level and not just about who's the better seller. Because of this, it's easier to make a better judgement call as to who's worth trusting and who isn't. Just use the same common sense as you would with any other financial transaction and you'll be fine.
All that aside, it's not a buy and sell community, anyway. It's about sharing of knowledge and opinions and every now and then some members help out the others.