How are you planning to market the computers? In person, online, over the phone? Think about how you can reach as many good candidate purchasers as possible. Try to avoid people who are unlikely to buy (to save both you and them a waste of time).

ebay is good if that is the type of business you are looking for. Make sure that you know what the machines will sell for before you purchase them, so that you don’t have inventory sitting around that you can’t sell at a profit. If you do make a bad purchase, just sell it for what it is worth and take the loss, rather than waste your time trying to sell it for more than it is worth.