FAQ: What prevents someone from claiming multiple POIs ?
All hangouts are simultaneous. The protocol relies on the fact that you cannot be in two spaces at once without anyone noticing.
FAQ: What happens if I miss a hangout ?
Hangout session happen at monthly intervals and each round gives you a new anonyumous/pseudonymous token, not traceable to your previous one.
FAQ: Couldn't people just bribe each other and be verified by multiple hangouts ?
The benefits of bribing groups to gain extra POIs will saturate pretty fast, as with any other pyramid scheme, and the POI economy should have a relatively small amount of scam-POIs in circulation.
FAQ: Could you expand a bit on how the anti-spam mechanism works?
The randomization makes it hard to gain control of entire groups, but controlling 2x or more the total number of users is a way to bypass that. Anti-spam deposits make it very expensive to perform this attack.