Agree. I had the same experience -- some items sold for prices that I would not personally pay for used. I sold things like ink-jet printers, computer desks etc. Still, I'm surprised someone purchased a mattress.I can't believe the stuff folks will buy off of craigslist or kijiji. We sold a mattress there once, somebody paid me like $100. Granted the mattress was good quality and only about a year old - and we're clean folks. But still, not the type of thing I'd be buying used. I scoffed at the idea - and yet it sold right away. My wife recently sold a 'it's not a blanket, it's a duvet cover' thing she didn't want anymore on kijiji too.
Conversely, I've picked up some good deals on those sites too. I collect antique books, some guy was unloading entire cases of some old, valueless legal books from the 1800's. I drove a few hours and paid him $40 for them, he'd have likely landfilled them otherwise.