I personally do not, however I have made some income and read plenty about people who do. In theory it's pretty basic, but the tough points are getting around the targeted games economy and banning system, while making sure the game is strong enough to support this. I do not think that Diablo3 is a strong enough game to make a living off of, WoW is certainly one of the more revered and heavy money makers.
A friend of mine does this with selling WoW accounts because Honorbuddy is just so great at this kind of stuff now. The roundabout version of what i'm trying to say is you want a good number of accounts, a strong, or fleet of computers that can run these games smoothly, either healthy farming levels rotated out, or insane farming with isolated accounts you don't care about losing, a good buyer (this I can not help with), and of course good money, character leveling, or whatever substance attaining method in which you sell. I'm not quite sure about this part though, but some people go to some sketchy lengths to protect themselves against Blizzard possibly linking accounts to eachother, using things such as virtual machines, dedicated hosts, proxys, vpn, and so forth. It's a very simple money making investment, however small mistakes can add up. If you know these already and are looking for more specifics, I apologize. I hope you find what you're looking for.