Im looking into working for myself as a courier?

ive looked on the net at many sites saying you can earn this much a day and whatever but iv heard it all before. what i would like to know is that can you earn a decent wage from doing this or are they just after my 40 quid and will send me a load of rubbish in the post that will get me nowhere have u used any of these sites? are u a courier? am i just dreaming? lol all answers welcome thank you.