What you're thinking of as "blocking spammers" I'm thinking of as "preventing DDOS." It's much easier to determine if there's too much traffic hitting a node o

What you're thinking of as "blocking spammers" I'm thinking of as "preventing DDOS." It's much easier to determine if there's too much traffic hitting a node or leaving a node than to determine if the traffic is "good" or "bad." I haven't seen anyone describe a way the system can generate "bad" traffic yet (that doesn't just degenerate into dumb games you could play without Duplex involved, like booking a reservation with your own phone and then just not showing up); generating too much traffic is a far more easily solved problem. But on the topic of discerning whether the traffic is "good" or "bad:" this is actually a circumstance where the mass of data Google has access to that seems to so frighten people works to the advantage of the business-owner. Identifying bad users of the system could be done, for example, by collating data on reservations with geolocation data gleaned from maps to note there's a pattern of a particular user booking reservations they never use. Google can then just deny them access to the service to preserve the service's reputation.