Purchasing a used mattress it a risk. I have purchased used mattress' during my 20s and never had any problem. Just go over it the best you can with a flashlight and ask the owners lots of question! If they start acting funny or something doesn't feel right just bail. Also, I have worked for a 4 star hotel for over 6 years, if I had to look at the lesser of two evils.... I'd sleep on a used mattress from Craigslist before I slept on one at a hotel.