The buyer put two orders: first one for 3 $20 bank notes and second time for 2 $20 same bank notes. I noticed the unusual behavior of this buyer: he bid many $0.01 with free shipping items, looks he used this way to accumulate his eBay score. So when he put the second order, I told him I need to wait the first order arrive before I ship the second order. He said he needed them fast, but he can wait. The next day he told me the items arrived, and to confirm I asked him what are the serial numbers he received. He gave that to me, which is correct. I sent the second order, but this time with tracking number. 20 days later, he opened case claiming not received the first order. eBay firstly made decision in his favor because of no tracking number, but reversed the decision after I called in to appeal and explain. I got my money back and hopefully the buyer would be removed by eBay.