If terms were agreed upon in chat before the fight, you can report if it's broken.

I had to file a report due to this reason, and they got back to me within a day asking for a little more detail (zone, terms, time of conversation, etc). While you'll never truly know the outcome, the guy that I reported was no longer sporting the ring in question after a few days. And even checking the lodestone isn't complete proof as it likes to upload gear funky sometimes, but it made me feel better not seeing it