What you do is buy a giant server for a couple hundred thousand dollars, then you program a self-aware AI to automatically search the CS for good deals. It will probably take about 1000 man hours of programming to put together a good algorithm to check all prices, forecast how many players are currently farming these items and also crunch the data to see when the new expansion is coming out based on twitter feeds, forum posts and facebook posts. After that its easy, you just let your self-aware AI automatically buy at good deals, calculate the optimal sales price and relist. Just be careful if the AI starts wanting to build other merching machines, because its probably secretly trying to build up an army of robots to take over the world. If a beefy Austrian guy shows up at your door naked telling you he needs to protect you and that he will return shortly, all is probably lost.