>I have the idea (maybe wrongly) that people don't often use the USPS for scams because committing fraud by mail is a federal crime, and the postal service actually has inspectors with police powers who don't fool around once they get on the scent.
Apparently, mail fraud[0] (via USPS) and wire fraud[1] (electronic communications) are both Federal felonies punishable by a fine and up to 20 years imprisonment.
Perhaps the difference would be FBI investigating instead of the postal inspectors?