It's also safer than buying it off the streets (aside from dealing with gang members), there is no telling what you are buying (they probably don't know either).

While it's true that everyone mistrusts each other. Sellers are also competing with each other to offer the best products with the best prices, putting a huge amount of effort to build the best feedback ratings. A world away from gangs using extreme violence to increase turnover (you would think that factors into the priorities). I'd feel safer buying from DreamMarket than I would Ebay.