To start off this article I'd like to express how easy it is to check if the person doing your plumbing is a qualified plumber. All you need to do is Go on the PGDB (plumber, gasfitter and drainlayers board) website and type in there name.
In New Zealand any person working on plumbing (except for minor jobs on your own home that you have to live in) needs to be licensed under the PGDB. Anyone caught working without a license will receive a $60,000 fine and for good reason to. In the past month alone we have been called out to several botched handyman repairs ranging from uncompliant dangerous piping being used to traps being installed upside down and siliconed over in attempts to get it to stop leaking.
The troubling this is you can't always tell if a handyman has done a good job once they've finished, you may only realize once the leak has caused damage and things need to be replaced
As funny as these sights are some times It's always a better safer option to call a professional the first time and paying a professional will always be cheaper than paying a handyman ten a professional to come and fix it.