So assuming you sold this as used, that sucks I feel for you. However if your one of those scumbags who sells used things on Amazon as new I have no sympathy and I would happily report you for my money back. (I have encountered this maybe twice in all the electronics I buy on Amazon)
If you want to sell used things you have opened, flag them as such on Amazon or go to Ebay. I buy from both places and will always take a deal on a cheaper gently used item if its disclosed up front.
Edit: For clarity, FTA > "To this day, I have no idea what he claimed was “missing” from the package. I even included all the original plastic wrap!" He opened a factory box and unwrapped the product. How else would he photograph all the parts with the kit?