I am self employed as a gardener. (I retired from my previous profession)
it is a hobby really. Mostly older people. I accept cash or cheque.
No receipt required as transaction is there and then , and no credit control activities are required.
It keeps my fee per hour lower than average, as i do not have to add in unit costs on all the additional tasks of excessive paperwork, accountancy fees etc.
i do my own accounts and submit my own tax returns annually.
I used to work for HMRC sometime ago and can advise that it is not a criminal offence to pay in cash or fail to enquire about a trades tax affairs, unless of course one is a chartered accountant, and only then if they are fiddling on behalf of a tax paying client.
I work alongside many trades and we cross refer.
I would not ask them about there business, anymore than i would ask about a customers tax affairs.
And the best thing about being self employed i can pick and choose my customers. There is more business than i can deal with, as is the case with most small businesses