From Guardian article:
The website says that its fair and unbiased ratings system allows customers to select tradespeople independently.
Finding a good tradesman is never easy. These websites sell a service to the builder, gas fitter etc so they will do what ever to protect their customers. I am always very wary of such sites. As you have found what they promise and deliver do not seem to quite match.
As for your bolier man quoting inc VAT when it sounds like he may not even be registered. Is he Gas safe, was Corgi.