We're taking part in TechStars startup weekend and have read through your feedback on this forum regarding websites like Rated People or My Builder and understand your frustrations with them.
The root of issues with these sites is trust. Specifically a lack of trust on both sides.
Customers are fed a diet of dishonesty by media such that their default position becomes that all trades people are theiving liars. As customers have no idea what is require to effect their desired outcomes, when person A says do it this way, and person B says do it that way they (even though both are proably correct) the customer is left feeling like they are being ripped off through this pre-conditioning. They have insufficient technical knowledge to appreciate that both can be correct and that, really, it's simply a matter of personal preference for the customer. Nonetheless, the negative stereotyping is reinforced due to simply offering choices.
Trades people distrust customers too. What no one talks about in our industry are the serial arseh0les posing as customers. These sites often attract them because they are given a fresh new set of victm tradespeople many of whom are inexperienced and cannot either sense or defend them selves againt the BS.
If you wish to put together a site that breaks this mould, then may I suggest you consider first how you will police and protect the innocent parties from both rogue traders AND rogue customers? To me, the first thing you have to do is have a three strikes and out policy with zero tolerance. You need qualified people to inspect and adjudicate and decide. If the guilty are named and shamed and banned by every means possible then you will begin to see confidence developed in the brand and concept.
So, at the core of all of the above sits a methodology that has, at its heart, measurement for how people FEEL treated. Without it, IMHO, you are wasting your time because measuring only process & procedure will not capture the customer experience.
Have fun...
PS I used to do this stuff