Interesting discussion. My son worked until recently as a self employed kitchen fitter in a two man team. It would have been difficult for him to fiddle taxes or VAT (although he was barely making minimum wage so VAT is not really relevant) as the official price quote was given through the kitchen firm and proper receipts were handed out. However the quotes always stated that the payments should be by cash or bank transfer at the completion of the work, and cheques were not accepted. This was for two reasons, there simply was not enough profit to build up a reserve to cover the time a cheque takes to clear and other workmen, plumbers & electricians needed to be paid, and secondly chasing up payments generally was a massive problem. It was the main reason he stopped the work and trained for a different trade. Every time he had to return to a house to try to get payment, he was spending his own petrol and time and it was very stressful.
I know decent gransnet people pay when things are due, but believe me, not every one is like that!