I have often wondered just what they do with those mattresses that come back. Here in Canada even most charities will not accept a used mattress.
I'd be worried about bringing bed bugs in. The store I bought my new one from last year will pick up your old one to dispose of it, but not with the same truck that brought your new one. They send another truck and crew a few hours later to pick up the old one from outside your house. This is to keep from having an old mattress introduce bed bugs into their new mattress delivery truck. I thought that was pretty smart.
A friend of mine had a serious bout with bedbugs two years ago and she had an awful time getting rid of them. She had to throw a huge amount of stuff away and the whole thing took at least a couple of months and cost a buncha money.
I went with her to talk to the bedbug people (exterminators) and what they told us really creeped me out. He said most people never know how the bugs first come in. They can come in in luggage from an infested hotel (even VERY nice hotels have been known to have bedbugs -- cleanliness and niceness doesn't protect against them, and all they need is one guest who brings them in in their luggage or person) or on the clothes or possessions of a person who has picked them up at someone else's house or workplace or anywhere. Laundering doesn't kill them, not even in hot water. Regular OTC insecticides don't kill them. They and their eggs can go dormant and crop up months and months later. You have to buy special insecticides to get rid of them and be thorough and hope for the best. They are a VERY big deal and are so small they are hard to see and can be mistaken for specks of dust. They get in clothing, wood furniture, upholstered furniture, drapes, baseboards, carpets -- virtually anywhere -- and you don't know you have them till you start getting little red spots from their bites, and by then they're everywhere.
I was so creeped out that I had my regular exterminator treat my house for them, too, as my friend was in and out all the time, and who knows if she was carrying them on clothing or purse or whatever.
EWWWW!
This was my first, and I hope LAST, encounter with bedbugs.