Is it the one in the black bag? If it is it's a good one. I would buy all new tubing, and parts to go with it, but the pump part just clean it. When Twas born I had to pump cus he was early, and they let me use the hospital one, and then after I rented one from the hospital. So it can't be that unsafe to use a used pump if a hospital will rent them out.
Anyways I pumped both sides, but that was cus T couldnt empty my breast, so I would have to pump after him. But you dont have to pump both sides I think if you unhook the tube, and plug it you can just pump your one side. I would at least look at it. Check on the net what the new one is like and then compare. But I wouldn't worry about using a used one if you get all the tubing and stuff for it then you should be fine. I got tubing and stuff from the hospital, but you can buy it anywhere.
Good Luck....