Sadly there are a lot of scammers out there, people who will trick you into thinking that they're legit. Here are some ways to spot a scam, as well as some websites I would avoid.
1) The biggest giveaway is fees, no should not pay to work, but get paid. If a company asks you to pay a startup or registration fee, then it's not worth it. Companies invest into their employees, not the other way round.
2) Too good to be true? It most likely is. You will not make £500 a week from an hour's work, it's just not real.
3) Avoid applying for jobs which don't actually tell you what the job is. It sounds silly, but there are adverts which simply say how much money you can earn, and not what the job is.
Right, now you know what to look out for, lets move on to what you should avoid.
http://www.treasuretrooper.com/members/home (At first looks legit, but then they refuse to pay)
www.kleeneze.co.uk (Have to pay a startup fee, no guantee of earning an income from your work)