At one time, a new furniture store owner often would have a second used furniture store in poor neighborhoods or ghettos under a different name.
Sometimes the trade-ins are actually antiques of value. I recall a know-it-all appliance store owner grousing about having to pick up heavy iceboxes in the older sections of his Appalachian city, when delivering refrigerators. I let him know that those iceboxes are highly desirable vintage items with price tags as hefty as their weight. It was sweet revenge for years of his denigration when he sighed and said that it had been over two years since his last one. Might add that his business practices eventually lost him the store...
In many areas, it's illegal to sell used mattresses but it may be legal to recycle their components and sterilize the stuffing for insulation or other reuse.