I have used Amazon, Newegg, TigerDirect, and Ebay. Most recently, on Ebay, I purchased a now discontinued printer, a new case fan, a new Corsair dual SSD bracket (for relatively cheap), and a used GPU. Overall, I have been satisfied with my purchases and even more satisfied with the savings. It pays to be a little careful, but keeping an eye on the seller's ratings helps in that regard. I use Amazon the most, because it's much easier to find what you need, and their returns are, for the most part, fairly hassle free.