Hi Chuckl007,
I don’t know anything about the retailer you are buying from so this would be one of those situations where you would need to use “best judgement” and decide whether the story is believable. I would also want to know the date the mattress was manufactured.
Phoenix
ADDED: Post #2 here also has some suggestions about checking a mattress that may be used and as Jeff suggested in the next post I would also ask them to remove the plastic (mattresses can easily be rebagged) to check for signs of use, stains, or damage.