A customer's perspective: I started looking in yellow pages, but found that useless. Then I started googling, but found it brought up too many traders who weren't local. Then I looked at find a trader type sites but most of them I didn't like because they wanted me to pay something although I had no idea if the site was any good, or they got a number of traders to pay just to quote, which seems a bit unfair on the traders. And then want 10% of the price for the job from the trader!
Then I found trustatader, which seems pretty good. Lots of customer reviews available that look real (a spread of dates and names). Spoke to an electrician who used it and he thought it was great. The trader pays a fixed fee, not per job. So currently I am using that. However, I will check out checkatrade since a few of you rate it highly.