I started a merchant's guild/cartel in Wrath of the Lich King.
We'd agressivly buy out items that moved at a slow enough pace that we could get them as they went on the market, but were bought out fast enough we could usually make the money back the same day. Frost orbs and their ilk were the best shit for this. Then the guild would go in turns overcutting each other to drive the price up. So Hebe would put his up for 1000g then Schlomo would do his for 1500g to cause Hebe's to get bought on as Rosenthal put his up for 2000g and so on.
Appearently it was against the ToS or something and we all got banhammered as a result.
I'm trying to figure out Warframe's economy, but with a lack of automated selling services like an auctionhouse it's hard to get a grasp of.