From what banking perspective is that?
Tax avoidance sod all to do with me am paying for the work.
Also shops do deals on cash as they avoid debit/credit charges.
No, shops don't do deals on cash to avoid card charges, they do deals in cash to avoid it going through the books. Cash is MORE expensive for a business to pay into their account than the cost of a card transaction.
Tax avoidance does effect you - The cost of it means your other general taxation is higher and your public services are effected. You might "gain" by a bit on the odd occasion you need the services of such an individual, but you will be losing out in the long run.