Part of the crazy markup in the mattress industry might be in the non-returnability of them. Manufacturers need to price in the fact that some % of them will be returned (read: given away for free) because no one wants a used mattress that might have bed bugs or other unknown substances.
I think it was covered either in the article or one of the comments here. But the companies don't really care because the mattress cost very little to make so they don't really make a loss if the customer was never going to buy it anyway.
The amount of effort and time required would just barely be covered by the profit. You also have to store it until sale. That's probably what keeps this from becoming a widespread scam.
I think you underestimate people's desire to scam the system. Buy $1000 mattress, leave in box, "return" mattress and get $1000 refund. Sell online (instead of donating) for $300-400. Rinse, repeat.
The "rinse" part is where it gets tricky. There are firms that track returns (at least for retail). I've seen people have their returns straight-up denied.
