Just add quick feedback with stars rating, and maybe short text, but it's not going to be easy to prevent fake reviews.
Preventing fakes is a major issue. Even if we required a valid swap ID then it's very simple for an exchange to provide however many it takes to flood the reviews.
I'm not sure how feasible it is in the case of Orangefren, but for example, Exolix has the option of adding an email address for sending order information. Only after the transaction is completed, you will receive an additional email to evaluate the service.
If nothing else, fake reviews are avoided, even for users who have not used the platform at all.
I assume that such a thing is very difficult to do as a partner aggregator.