Ok so these scammers are clearly been ripping people off, but one of the biggest problems im hearing alot around my area is customers accepting work from "diy" cowboys who are claiming to be trademen.
And most people know they aint trademen but still offer them the work because they think they saving 60% but infact end up having more issues and having to pay real tradesmen to come back and re do everything at extra cost.
It really is beyond time that all tradesmen should be qualified, registered and authorised as this would be easy enough to implement.
When I worked in France I had to register and show my certificates and such like with the local chambres de métiers who then issued me with an authorised and duly stamped carte d'identification. Any work I carried out, people could and did ask to see it - as could any passing police officer believe it or not. In fact, a couple of Gendarmes actually turned up at my door once asking to see my papers!
All sounds a bit big brotherish and over the top but, it practically wiped out getting conned and anybody that did only had themselves to blame as there was a system in place that helped protect both worker and customer from those cowboy con artists scammers.
Don't limit the friends you haven't met with arguments you'll never have.