I have also supported the flag. What I see is that payment was made upfront. I don't know if this is usual or what because I have never participated in review but I suppose that if the payment was made after submitting a satisfactory review instead of upfront, this wouldn't have happened. However, I understand that maybe the payment was made this way for simplicity and convenience.
I believe one of the reasons why the campaign manager and the project team paid upfront for the review was because the review itself will require participants to spend a few dollars in order to successfully try out all the features of the project.
The project had good intentions so that participants wouldn't complain about not having funds to pay for the review service. It's just so sad that someone out there decided to use that to their own advantage by scamming the $90.