Understanding PTC Sites

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I have joined a few PTC sites and I know that it takes a while to earn but a lot of them are hard to understand. How do you know what they pay you per click and do some of them false advertise? I was looking at one site and they are talking about how much they pay in euro's. I couldn't understand exactly what price they were talking about. They make it seem like you are getting a dollar a click when really you are only getting .001 per click. What kind of input can I get for understanding how much a site pays?