Just curious though, how do they catch people? Would they be able to look at phone records and use that as evidence? Would they follow someone and photograph them? If they don't know their full name and address how would they get 'em?
Well I found out that I cleaned the windows for a local tax inspector. I didn't know that to begin with though.
It didn't make any difference as everything we earn, including tips given is declared.
If they do investigate you then they can make your life very difficult. You get on the naughty step and they keep calling you in for interviews.
As has been mentioned, you need to register your business and pay tax on your earnings to be legit.
Disgruntled customers, other window cleaners with a vendetta, nasty neighbours etc can all make an anonymous telephone call to the local receiver. They don't need to have proof, they just need to make a suggestion that something doesn't add up.
A service supplier could publicly brag about the car he is driving, but his wage indicates he doesn't earn enough to have it.