It's most likely based on the honor system. I mean, if you're willingly paying a visit there yourself, you came there to get work done and have some fun doing so, not to actively game and exploit the system. Plus, the cafe only has 13 seats, and the website says that the space is usually a photography studio (and only operates as a writing cafe during off-peak hours), so whatever irregularity that comes up can probably be dealt with on a case-by-case basis-- this isn't a public web app that needs to automatically defend itself from all sorts of attacks from any random hacker in the world.