Used computers are usually refurbished Dells, HPs, or some other name brand that has been "refurbished." That is, they have some crap soldiering job on some burnt up connection and a fresh coat of paint. They still have the tag with the serial# of a MS OS, so whomever refurbished it went ahead and reloaded the OS without all the crapware. Aside from the hardware being suspect and the microscopic HD, they're better than new. Often, a mom and pop store will have a dozen stacked up.
The computer I'm using is of this nature. It only has a 40 Gig HD, which ain't much. The PS2 connection for the keyboard doesn't work. That must have been the original failure for which it had been refurbished. There is a reason the military does all of its electronic repairs in house. When the Army sent its radios out for repair, they came back looking like new, but they still didn't work. I got lucky with this one. The USB ports work fine.
Right now, you can go to Toshiba's website and buy a Window's 8 Pro laptop for $450.00, and that will come with rights to downgrade to Win 7 Pro. If you want a machine with Win 7 Home edition, it will cost you about $100 less. Not all models with all processors can be configured with Win 7, but Toshiba is really good at making it easy to find what you want. Trying to find Win 7 Pro on HP and Dell's sites is not as easy, but they still offer Win 7. MS has to allow computer vendors to do this, because their new OS's tend not to play well their larger customers' networks. They don't give a crap about you and me, but companies like Toyota and ADM buy a lot of MS software, and have the means to go elsewhere.