How do you know a Pro did it? or are you just looking for an excuse to bash licensed plumbers?
Everyone wonders why some threads erupt into name calling. Your post is a prime example of why. Your asseration is most likely to ellicit more than one reply from a "Pro" that is insulted by your comment and rightly so. If we are going to keep track, I'm willing to bet that us "Pro's" spend more time fixing hack work done by diy'ers than the other way around. But who's counting.
Why does it seem like plumbers are the ones claiming insult and getting all defensive? Yet you bash DIYers. That's not just my observation, but one of several GCs that I've worked with over many years.
A real pro would realize that all fields, including theirs, have a significant percentage of hacks. Mine's got them, concentrated in the geotechnical area. I don't make excuses for them and neither should you. In fact I've reported mine to the State licensing board more than once.
With regards to the DIYer screw-ups that you end up fixing, my guess is that most are your customers who didn't realize that they were making a mistake, but once they realized it called you to repair it, then gladly wrote you a check. Compare that to the plumber, electrician, framer or painter hack that knew he was cutting corners, covered it up and never considered telling me about it, then gladly takes
my check.