Hi Exhausted,
All fire barriers other than wool would have something other than a viscose/rayon material (such as the thistle) or polyester in the fire barrier so your “warning” would apply to almost every mattress sold in North America not just to Saatva (which is more transparent than most manufacturers about the materials in their mattresses … see post #1 here). If people were to follow your advice the only mattresses that they would be able to consider (at least without a prescription that would allow a manufacturer to make a mattress for them with no fire barrier at all) would use wool for a fire barrier because all mattresses sold in the US are required to pass the fire regulations. If it is a viscose/silica fire barrier then for most people it would be safe (see post #2 here).
It would be very uncommon for a store to refund a returned, used, or liquidated mattress and there would be nothing that a manufacturer could do either because these types of purchases of a mattress that has no warranty are always “buyer beware”.
Phoenix