I bought an invisible pen, with a small blacklight. I put my initials on the box or tag or whatever, which only shows up with the light. Best three dollar investment ever. Recently had a buyer tell me I sent her navy shorts, not black. ( underarmour). I apologized and told her to send it back and I would refund all monies, including return postage. " and oh, by the way, my initials, first middle and last name were on the tag." All of a sudden, she wanted to keep the navy shorts I had sent her