As an online retailer, we don't actively use review sites to request customer reviews as they cost an arm and a leg. We trailed trustpilot for about a year but decided to stop as we didn't feel we were getting our monies worth.
What I'm saying is the only independent review site you will find reviewing our business is trustpilot.
Remember that customers will not generally seek out a review site to leave a good comment, but will be more than happy to actively leave a bad review on every review site if they have a bad experience. Unfortunate this means that you will often find plenty of bad reviews but less good reviews. You only have to look at courier reviews to see what I mean. This is does not necessarily reflect the truth about a business. The bad reviews may be a tiny percentage of the total customer base and let's face facts, no business is perfect and there are some customers that just can't be pleased no matter what you do.
I think the best way to gauge an online business is to look for simple clues such as a valdi UK address, a valid UK telephone number(pick up the phone and speak to somebody), do a Whois on the domain name to see who it's registered to, when it was registered and what the registered address is. Always look for HTTPS on any pages where you are entering sensitive information including your name and address.
Check terms and conditions. Many scammers will not be aware of the distance selling regulations and will often have terms such as no returns, or they will charge a handling fee.
Check for grammatical errors. If a business can't be bothered to write proper English, then I doubt they will be bothered when it comes to customer service. I'm not saying discount a site if you find a single spelling error though
Also always use a credit card for purchases over £100 and NEVER pay by bank transfer. A legitimate business would not ask you to pay by bank transfer if your card is declined.
Remember that just because a site ends in .co.uk and advertised Royal Mail delivery does NOT mean they are a UK business.