As far as working for cash goes, I've done it, I still kind of do a little cash income now but I hold the cash or I spend it, really cash earned by working can't really be used for much other than groceries & bills.
The thing is about working for cash is, there's a limit of what you make before filing a w9 but.... If I fix computers & sell them getting cash there's also a loophole for that under the tax laws like there is for many other things.
If He's working for someone for cash it's a contract, he does a service for a fee. Really the thing is, it's a contractual agreement whether its a verbal agreement or written (These are usually verbal) it's really noone elses concern, it definitely depends on the type of work he's doing. If he does odd Jobs he's definitely got nothing to worry about. If he's a mechanic or a welder or something like that he's all set too nothing to worry about.
The IRS isn't worried about him all that much, they're concerned more so about 10 different men named Jorge Sanchez all working on the same ONE Social Security number that belongs to a guy named Brian Smith. Brian smith is the one that would have some explaining to do whether it was done by his knowledge or not.
The IRS is also worried about that employer that's cooking the books to pay people in cash.
Now if he goes and makes a dumb ass decision like tries to pay for a brand new honda civic in all benjamins or something like that that's when he's going to wind up being investigated.
Also his credit must be Sh**.
If he's just not filing, The IRS will eventually figure him out & pay him a visit to do all his numbers they'll deduct his check if he owes but sometimes not sometimes it's a warning.
If he's not laundering money & not cooking his own books it's usually nothing major.
Personally I'd much prefer to do a nickel in a Federal Penitentiary for tax evasion than 6 months in County for assault and battery.
Either way it sounds like he really doesn't have anything serious like prison time to worry about.