I was very nearly at the "had enough of this discussion" stage myself. But felt compelled to counter this last comment from someone I thought had more understanding to be honest (going from previous posts in other discussions)
I have never been what is loosely described as "white van man" but I do subscribe very much to the "live and let live" philosophy. Why? simply because it is, "none of my business". I wouldn't dream of informing the authorities on any matter except perhaps child abuse.
The whole self employed system here in my opinion is a shambles and needs to be completely overhauled. Historically, I ran a small/medium sized business in the UK for 30 years and paid my taxes according to the laws etc. I won't deny the "laws" were there to be stretched a little on occasions. But here, from what I gather, an artisan cannot survive without doing an average of 50% of their work on the black. It is simply, how it is, again, from what I gather. The ordinary french person (Joe public) know this to be the case and accepts it. There are all sorts of reasons why this is so, apparently. One reason is, that all sorts of benefits are available if earnings are below a certain level. An incentive to stay below that, obviously, for those that are "in the system" and know what they are of course (another story)
A point to consider, when doing "a cash" job is not only a risk for the customer but for the tradesman as well. That in itself, surely, is an incentive for "the builder" to do do a good job. In order to get paid at the end of the job? Because he/she has no paperwork to show if things go wrong. There are just as many bad customers as bad tradesmen. It's about trust at the end of the day.....mutual trust!!! Most of my old customers went on recommendations or gut feelings (instinct)....apparently?
The question of insurance is somewhat blurred, I have heard of many cases where the customers have a had a real fight on their hands and this can last for an absolute age. Is it not better to build up "trust". French "normes" from what I gather can leave a lot to be desired in certain cases. A good example of this, and one that should be very obvious, is, rendering to the ground??? an absolute no, no in the UK for very good reason, it fails every time.
It makes me smile when I hear people say that in order to be "respectable" you have to pay enormous amounts of social charges. The customer is paying those, not the tradesman. He is too often just the poor "unpaid tax collector" at the end of the day...please wake up people! What benefits do you get from these huge tax liabilities. Well, if you are civil servant with 3 children you can retire in relative comfort at 50?? I bet a whole heap of you fall into that category.
My advice would be, if it's possible to give little jobs to begin with and build up that trust. Or perhaps employ someone who knows a thing or two about building to supervise a project. Too often there is a penny pinching mentality from the outset which often ends up costing far more in the long run.