Blocking a seller from my site

[sgar4056]

This seller sold me a silver pendant and I took it and had it tested to see if it was silver and it was not. I told him that I wanted to send the pendant back to him and get a refund and he said that he don't understand why I want to send it back because it was silver and there was nothing wrong with it. I am paying an extra 8.45 to send it back to him because he won't use the program e bay has to send things back, it would have been a lot cheaper for me. He sent me a refund but still continues to aggravate me and I just want to block this guy from coming into my site, I am also an e bay seller.