My concern is that in your contract there were probably never any promises with the performance of his picks.

After all, the gambling industry is based on complete chance in some respects. And whilst tipsters try to swing these chances in their favor, they usually won't go out of their way to guarantee winnings which I assume is the case here.

So unless you have proof that within your agreement he had claimed something regarding the performance of his tips or something along the lines of that, all you can say at the moment is to warn people to stay away from him. Mods won't do anything about it, because that's not their job.