dont worry, we/she know its the minority that spoil it for the rest.
I do think there should be a national register to post your location and who you have had that was a good tradesman in any trade. Only listing the good ones would be the way, listing the bad opens it up for anyone to slag off a competitor etc... so if only good it would be helpful (although not foolproof but if you had to submit your own verifyable details to post then that should keep it clean)
Or maybe there already is one that is not widely known?
Since he installed it in the first place, and it was part of the original job, he shouldn't have charged - I wouldn't have.
If she has any more problems, I only live a few miles down the road and will come and have a look and charge for parts and a slice of home-made cake and a cuppa to redress the balance! I used to be a christian before becoming an atheist!
Good as those schemes are, they are only listing a very few firms and most fit a strict profile of those who charge a lot more than average.
There are many very competent and reasonably priced firms, mostly sole traders or man and boy, where they have plenty of work to do and dont have to APPLY and PAY for those schemes just because they charge so much that they dont have enough work to do.