They basically have great search engine optimization. Most of the sites are in reality the same people and each site boosts the search results for each other. Lot of work but they get a lot of suckers that send them credit card details and bitcoins.

easy to pick out the sites to stay away from: 1) all high ticket items. 2) no go between/escrow. 3) No voting system. 4) beautiful pictures of product 5) high quantities available. 6) no cool people hanging out on the site