Napa doesn't use the thermal ink printers anymore. Maybe some stores still do, but the on eI work at and the other local stores switched to regular ink. The receipts are printed on a regular laser printer, the same one you might have at your office.
The store takes all defective/warranty items and sends it back to the warehouse/manufacturer. The warehouse/manufacturer makes the decision to refund the money and will reimburse the store for the cost of the part. So if you try to return a part, the store shouldn't really care that you're returning it as long as they know they can get the money back from the manufacturer. If you try to return something and the store knows it will have a hard time getting the money back, they may try to refuse to take it back.