Ubercart

I'm working on a site in which users can pay each other for services rendered. I want the site to take a percentage of each transaction between users.

I want the payor to be able to write reviews of the payee. Further, I want to require the payor to write a review of the payee, and I want the payor to ONLY be able to do so AFTER making payment. This is to prevent the payor and payee from arrangement payment offline so as to avoid giving me my percentage.

I was referred to Ubercart by a Drupal module developer. Any thoughts on how I can accomplish the above?

Thanks,

Jeff