Same flaw Da Ali G Show had...
As soon as Nathan gets a bit of fame and notoriety and the clients he's playing with are in on the joke, the humor is ruined.
Someone also said this at the beginning of season 3. But we have 3 strong seasons so far. And that's honestly good enough! Besides, all he probably has to do to maintain anonymity is move further to the Midwest.
If you want to hate something, go to imdb.