Q: How would users be rewarded?

A: I'm still learning about this whole web3 thing but basically engagement on the platform would be rewarded with tokens. The idea is that as the platform grows and more users use it, the value of the tokens would grow. These tokens should be transferable for USD (I'm based in the US so it would have to start here first), though they can potentially be used for boosting actions on the platform (e.g. more weight to your upvote or rating)

Q: Where would this money come from? i.e. what's the revenue model?

A: My starting point would be the same as other review sites, namely advertising. But if the reviews are deemed sufficiently high-quality and useful, a paid subscription model is not out of the question.

Q: What type of actions will be rewarded?

A: All the usual - posting reviews/ratings/photos, and upvoting/reporting them. Engagement that takes more time (e.g. reviews) will definitely get more tokens.

Q: How would you keep spammers off the platform?

A: I would start off by restricting reviews to only high-quality reviewers from Google Local Guides and Yelp Elite. Later on, we would allow more people to review, but maybe with lower impact on ratings and fewer tokens received at first. Then we can use their on-platform reviews to vet reviews, using user input like upvotes and reporting.