No...he isn't a 'tax collector' - he is a head auditor for a region of the country. He has caught some Superman 3 style schemes at major institutions. He really is doing a great service because he is incredibly smart and hard working and chooses to use those skills in the public sector.
What would making more money provide him? He has his dream job and job security.
There just can't be much joy in being a tax collector and if there is some anomaly and he does truly enjoy it, it's exactly that, an anomaly.