Making the world better, one answer at a time. Yes you can sell a used mattress is Washington State as long as the owner knows that it was used. No Retailer's can sell a used mattress. Outlet stores can not sell a used mattress unless the buyer is told by the seller that it was used.aking the world better, one answer at a time. Yes you can sell a used mattress is Washington State as long as the owner knows that it was used. No Retailer's can sell a used mattress. Outlet stores can not sell a used mattress unless the buyer is told by the seller that it was used.