Buying a used lift worth the savings?
I personally would wait for something newer to come around. The lift I just put in is 5 years old and saw very little use, installed when new by the same company that inspected it and removed it from the shop. With that history, I feel confident it's not going to smush me.
If you do decide to buy one of these $500 lifts, I strongly recommend hiring a pro to do the removal and installation. They can inspect it while they're at it. The money you save with the purchase can go towards paying the professionals and having peace of mind. You can sit back and sip lemonade (or beer) while they're doing all the work.