Buyer CLAIMS I sent wrong item W/O original packaging!

[dillsdprib]

I sold a Hot Wheels diecast car in new ORIGINAL, unopened package. Buyer wrote to say he received item on Jan. 22nd & posted feedback stating, "Great seller! Product as described" (I returned FB also). Today the 24th, buyer writes saying. "I’m disappointed. I stopped by my nephew today and he showed me the car I purchased him. It’s not the right car and it wasn’t even new in box. Was the incorrect one sent on accident?".

Buyer sent two similar pics of a DIFFERENT toy car, out of package, inside an empty brown cardboard box!

Considering it was a gift or not, wouldn't buyer (who happens to proficiently sell as well) open shipping box to clearly see if I sent the WRONG item BEFORE [giving it to someone] posting feedback that product was as described (which clearly identifies the product w/o opening)?

Not if it matters, but along the way, buyer initially wrote (on the 21st) to ask if I shipped item because tracking still showed 'Awaits item'. I wrote back explaining extreme lagging with USPS & that i'll begin a research case...  buyer never responded. I wrote to ask if he noticed research case status on tracking... buyer never responded. Then, the next day buyer writes on the 22nd like I initially stated, "I received the item today. Lol. Gotta love the Post Office".

So here's my question.. what would you do if buyer states he accepted item & posts feedback summarizing the product was as described, then turns around with claims it was the wrong item not new in box???

I have 100% FB, I have nothing to gain & have nothing to lose w/selling on ebay, but I take selling very seriously!!!

Thank you for any rational solutions!