This is the truth of the matter. Most errors/fraud for Joe-Blue-Collar revolves around refundable tax credits as there's a pretty good chance he's not even paying any income tax.

The EITC is particularly complex (blame Congress) and therefore error/fraud-prone, but many aspects of typical errors/fraud can be mechanically detected (is this a qualifying child? is this qualifying child being claimed on another return? is there undocumented non-W2/1099 income being used to support this claim?).