I'm not suggesting he do any thing criminal, or even illegal. There are avenues where a person can perform tasks for pay without becoming a full fledged business. Especially if it's not your primary source of income.
Ohio has declared this threshold to be $600.
The man I had do some repair on my RV last winter in Florida didn't advertise, worked for cash and come to think of it, I don't really know his name. He saved me having to take my 5er to Camping World for a minor repair. Saved me some money too.
Setting up a business takes skill in accounting & bookkeeping. And like they saying goes "In for a penny, in for a pound". They're linking all computers, comparing IRS to Worker's Comp. etc. You have to do it all. Not really worth it for a few bucks. In fact you'd be hard pressed to make a profit.
What I would do is take a box of chocolates to the park manager. Ask them if it's OK to help people change out a water heater element, rewind a spring in an awning etc. Then if it's all right with them post a phone number on the bulletin board.