It's not illegal to sell a used mattress although you must list the mattress as used and the mattress must be cleaned really good prior to the sale of the used mattress.
For example it could be illegal to sell a used mattress at a yard sale or estate auction etc unless the mattress has been cleaned and it's listed as being cleaned.
Some states may have different laws but in most places it's legal to sell a used mattress.
However buying used mattresses is not really a good idea because you never really know if a person got semen on the bed, got bodily fluids on the bed had infections etc.
I would rather sleep on my floor than on a someone else's used mattress.
You won't really go to jail for removing mattress tags.
The removal of mattress tags is not illegal for the consumer or purchaser of the mattress.
The removal of mattress tags is only illegal if the seller of the mattress removes the mattress tags.
The seller of the mattress would only likely get a fine and a court appearance is they are found to be removing mattress tags.
But as far as the consumer removing mattress tags there's nothing illegal about that.
You can freely remove your mattress tags without getting into trouble as long as you're not selling mattresses.
Nobody would know you removed the mattress tag anyway and if someone did call the cops about you removing your own mattress tag even if it were illegal the police would likely just laugh and not even show up to the call.
The police have bigger fish to fry anyway.
So remove your mattress tag if you want too as nothing will happen.
Mattress tags used to simply say they are not to be removed under penalty of law.
However now the mattress tags say not to be removed under penalty of law except by the consumer.
So as a consumer you can remove the mattress tag but as a seller you cannot remove the mattress tag.