I'm in no way affiliated to their project.

But I believe there would be a few possibilites for them :

- Pay extra to get feedback with people known as "experts" (UX/UI specialists), the "expert" would get and cut and so would them (this would provide a good incentive for people to leave in detail and high quality feedback). This is a win win for everyone

- If you get negative feedback, along the lines of "X needs fixed/changed/reworked", they could maybe teem up with oDesk or the likes (or do it themselves) to provide freelancers/experts to solve your issues

It's an interesting concept, it's not the most obvious thing to monetize, but it can be