Hi, I recently sold a model car in mint condition. Week later buyer says a small fault. What do I do? Proof? Scam? Help me.

[ladyonline1]

I sold a rare mint condition never opened or displayed model car & now week later buyer says it has a small fault & wants it rectified.
What do I do?
I have been warned that some buyers are buying mint condition models to replace faulty ones that they have already purchased then claiming that the one they just bought is faulty.
How do I prove? Is it a scam? What should I do?
It was mint condition & in no way faulty to my knowledge having been in storage for 7 years. I am an honest seller with a high rating.
If I get them to send it back & refund amount then I will be getting a faulty item that I don't believe was faulty & can't prove was mine.
Can someone please advise.