In the early days, we are paying Sats to bootstrap the review 'marketplace'. This is just to get the initial activity going.
Our plan is for Reviewers to earn enough sats from other users (if the reviews are good enough), such that they'll see a potential ROI worth posting a fee of their own. So, we plan on removing the initial bonus at some point.
This fee will be part of our eventual revenue model. But also like I mentioned in the OP, we're not entirely sure what the path to profitability is yet!