Hi Tabby476,
For the companies that allow you to donate the mattress to receive a refund then a copy of the donation receipt is usually all that they require. I would think that the assumption is that most people are honest but if someone did try to fake the receipt and if the company took the time to verify it with the charitable organization then they would be jeopardizing their refund which probably wouldn’t be worth the risk.
See post #2 here.
Selling a used mattress as new and without a law tag identifying it as a used and sanitized mattress or a rebuilt mattress is against the law and any reputable company wouldn’t jeopardize their business by taking the risk.
Phoenix