Survey Shenanigans

 I have taken to doing online  surveys. I was advised this is quite lucrative by those learned people who populate the Internet.Sadly, this is not the case.
Some of them suggest payment between 10P to £50 per survey and others offer vouchers or, alternatively, points that can be exchanged for vouchers. One of the sites I have signed up to pays cash which you can redeem when you reach a total of £40, so far, all the surveys I have done have paid between 10p and 20p.This would mean I would have to complete approx  267 surveys to earn my £40. Given that I am deemed "not suitable" for approximately 50% of them due to my age, marital status, lack of children etc I would need to attempt about 500 to earn £40. That's about 48p an hour. On the plus side they are sending me six or seven a day to do. The other sites are a bit more involved and take longer to complete but pay in points or vouchers which you have to reach £50 to redeem. however, I have completed 2 surveys thus far that have stopped half way through for which I have not been paid. I am informed by an error message that it wont count because of any of the following reasons,1, someone has already completed  the survey on my computer, 2, They detect some fraudulent activity. 3, I have completed the survey to fast. None of which are true. This means the  survey has been completed but I do not get paid. The companies do suggest this is important work and that my opinions count which makes me feel much better of course.
There are a couple of things that occur to me from their point of view.
firstly, They have to keep you, the survey panel,happy by providing  something to do but they also need to source companies that will pay them and allow them to pay the survey panel. there is probably an imbalance in this and i would guess they keep the panel happy by providing mock surveys just to keep them sweet. Secondly, I have noticed a tendency for the questionnaire to start of quite vague and general at first but then become much more specific about a particular service or product. Twice I have answered questions negatively and have been rejected as not suitable or survey quota full. I am not suggesting they doctor the answers to get the right results,but its not impossible.I have only been doing this for week so will have to see how I get on.