Hi there -- Thanks for your question. TBH there isn't really an established market for used mattresses. The reason is that mattresses are an extremely intimate product. While the act of sleeping sounds relatively benign, during sleep the human body also emits sweat and odors, some of which inevitably goes into the mattress. This is true no matter how clean it looks or whose it was -- and over the course of many months (let alone years) of use, it adds up. And of course, without going into too much graphic detail, this is to say nothing of other fluids that find their way into most used mattresses, along with dust mites, dead skin cells, pet (and human) hair, and the like. For most people, all of these things fall into the category of 'it's not so gross when it's mine, but it's definitely gross if it's someone else's.'

In light of these unique intrinsic characteristics of this product, there is little more demand for used mattresses than there is for used bathing suits. Since a fair price is ultimately a function of how much the seller could otherwise get for it, there is no question that a fair price should be at most a small fraction (eg, 10%) of what a new one would cost. That said, the reality is that their best alternative may be to have it picked up by a junk hauler or to drop it off at the dump, either of which would likely entail a fee, not to mention some amount of hassle. In many states, even goodwill agencies are not allowed to accept used mattresses for fear of spreading bed bugs.

Thus, IMHO a fair 'payment' is simply your willingness to come pick it up from them and take it off their hands, hassle-free. And perhaps even more importantly, they will receive the positive karma and clear conscience of knowing that their mattress did not end up in a landfill somewhere.

I hope that's helpful.