As someone who has been renovating and building and fixing for the last 30 years I absolutely never give anyone cash jobs any more and if they even suggest it they would be booted out in one second.
What I found was that the tradies who do cash jobs - essentially ch-eating* the country (which is US) - are also the same people who do things on the cheap in their work. Just think about it - cheats are cheats across the board - it's an attitude and that attitude is to rip people off.
I have a network of fantastic tradies all of whom have valid licenses (I checked) and invoice books. They give me a receipt and with it comes a guarantee of good workmanship. In the long run it is less expensive because there are no mistakes to rectify.
Oh - and about big ads in the yellow pages. Some of these guys are the worst. Don't judge by the size of the ad but by the reputation of the business.
*This word was not allowed by this forum so I had to break it up. Curious.