There is actually no rating ATM.

What you vote at the end of the trade is just feedback to the coordinator, but it's not shared (that info is stored in the coordinator itself and it might be tricked).

That said, I'm working on integrating nostr in some parts of RS and one of those is to create a coordinator rating system where none of the 3 parts (federation-coordinator-user) has to trust each other https://github.com/RoboSats/robosats/issues/1097