Craigslist transaction went south...

Hello,
Hope everyone is doing great. I have a situation here and I am hoping you guys can help. 
I have sold a home theater receiver to someone. We met at gas station and everything went fine. It happend on Sep 4th.  Today (Sep 15th)  i got a text from the same guy saying he just installed and the receiver is not working. He is going to take legal action against me. it was working receiver and i never had any problems with it. I don't know what to do now. . I am legal immigrant and working on visa.  Please advise.
Here is my ebay profile:  https://www.ebay.com/usr/manizthegreat