Two important things"
a) Reviews mean nothing in this industry. Suppliers are bad-mouthing each other in reviews and they use fake reviewers to up their scores.
b) Registration with any authority/council only means that they are legit as far as their rights to install and certify. It does not speak to their level of service and if things go south it is costly and time-consuming to get it sorted via arbitration.
So at the end of the day, consumers in this market are left to the sharks and it is a game of Russian Roulette.
But there are good guys out there, it is just not that easy to find them and hope that all the money did not make them go over to the dark side.