I'd also doubt very much the tensioner has failed, in what 25 years of the Fazer, I've never seen/worked (I've lost count of how many, 100's over the years) on one that has had a failed tensioner. This forum is full of post about the very thing.
If you're selling it only because of your chosen machinic telling you the tensioner has failed, ignore him, find someone else going forward and either reset it or rev the thing.
If you're selling it only because of your chosen machinic telling you the tensioner has failed, ignore him, find someone else going forward and either reset it or rev the thing.
Later