I’ve owned many Harbeths. The grills have to be removed correctly with a magnet. I have seen many Harbeth with ripped grills and damaged wood on the edges where the grills are.
It sounds like the buyer tried removing the grills incorrectly and wants you to pay for his stupidity!!
I was a Harbeth dealer and had a couple customers, (after being told how to remove them) still damage the grills and corner edges.
If I was a gambling man, I’d say that’s what happened...
Oh, and btw, I've done business several times with Brett, (yogiboy) and it couldn't have been better.