
One of the main things to consider is: how good is the English on their website? No matter how 'flashy' it may be (probably off-the-peg, mind), poor spelling and grammar on the website is a big sign that you're dealing with fraudsters who have no chance of writing a decent essay for you.
Also, are they making unrealistic promises? If they're charging you £10 per page, the writer is probably getting around £5 per page, and no good writer would work for such a low price.
This site is useless in terms of getting actual recommendations. If someone says X-site is great, they're probably the owner of that site. If someone says Y-site is rubbish, they're probably one of that site's competitors.
You'll probably be deluged with private messages - I know I was when I first posted here. I'd suggest ignoring them, taking some time to look at various sites (i.e. not just the first page on Google) and go with your instinct.
The sad truth is, many in this industry are non-English natives (nothing wrong with that) pretending they can write academic English (something very wrong with that). Try to talk to them, that way you can get an inkling for yourself.