I sold an old music magazine, which had some pages missing. In the listing I described it exhaustively, itemizing what was on every page and stated that it was best for someone wanting material on a specific band. The buyer is saying that it was described as 'like new; but it wasn't.
I have messaged him to the effect that the description was clear, but am I going to have to refund him anyway?
the best you can do is to get him (in Ebay messages) to describe exactly what the problem is. Then get him to open a case as not as described so that Ebay can adjudicate where he repeats everything he thinks is not right. If what he says doesn't match what you had in the listing, you have a chance of winning this. Only a small chance, though, Ebay Corp doesn't really look at facts most of the time.
That said, if it's a high value item I would immediately offer full refund on return, refund once it's back ok & block him forever more. It's not worth the stress to do any different.
LLjkk is right I would offer full refund on return of item in same condition you sent it in. Anything else & buyer will probably give you bad feedback & stars. Total pain & I'm sure you are right but the most likely consequence is they diss you if they don't get a refund. Double check it didn't say like new in your item specifics as it can slip through if you use an older listing as a template.