People who don't pay income tax ...

For some reason lately I've had people telling me about how they are avoiding paying income taxes. Just the last couple weeks my barber (going through a divorce) was telling me how his ex is filing for child/spousal support and how he is going to get away with paying next to nothing since he never declares income as he's an "all cash business". Then my landlord was telling me how he only declares my rent as income so he gets all the tax refund credits/child credits (he's a single dad, works 40/hours week for cash in an autobody shop).

I, however, work 40 hours a week and pay income tax, always have for my entire working life. Part of me wants to say 'WTF pay income tax like the rest of us do' and the other half of me thinks 'good for them they figured out a loophole in the system'. In the grand scheme of things the amount of money they are keeping is small compared to the amount of tax money collected by the government but still ..

TL;DR when people tell you how they avoid paying income tax, how do you respond?