I wouldn’t sweat it at this point. The only thing you may consider doing is buying it back at a fair price. Fair price does not necessarily equal what was originally paid (especially due to the trade).
Having someone call a watch counterfeit is certainly nerve racking. I’m sure many of us have had similar experiences, even though most of us aren’t “dealers.” I was once accused of selling a “counterfeit” watch to someone on this very forum. I was obviously worried that something could have snuck by me because the member had, and still has, a great collection.
This was not a run of the mill piece and I did my diligence when I had bought it and looked at other examples. Luckily I had taken numerous photos of the dial, movement, case, bracelet, etc. and nothing indicated it was “counterfeit.” His concern was that it was “too nice” and that when he looked up the watch reference there was a counterfeit website that sold them.
After a few hours of talking and sharing photos, he ended up apologizing. It was absolutely correct, and I had the laborious task of proving it without the watch in hand. Quite frankly, it was frustrating he didn’t do his own research before accusing me of selling a counterfeit watch, but I decided I had to just get over it because stuff like this happens.
In hindsight, I should have asked for the watch back because it was obviously priced too low... 🤔 water under the bridge