Believing the device's idea of where it is isn't going to help against any kind of serious criminal (get root, hook API, profit; and what about people without smartphones, anyway?). Triangulating a phone via cell phone towers might work, but that opens a whole new can of worms: you need the carriers to cooperate; it's a privacy nightmare; conclusively linking a Yelp username to a physical SIM card is not easy; and so forth.
True, but at the very least, we're reducing the set of all possible fraudsters and system-gamers.
How many of the fraudulent reviews on Yelp do we really believe are coming from fraudsters with this level of sophistication? My guess is that it's a pretty small percentage. Seems far more likely that most bogus reviews are coming from competitive small business owners, paid-off users, and other relatively average folk with a minimal level of technical understanding -- or even sufficient malice to drive them to become more sophisticated. (It doesn't help that Yelp may, or may not, be assigning greater weight to negative reviews unless/until a small business owner buys into their advertising).
