Thousands of companies in the all over the world wants to know what is people's opinion about there products.For that they are conducting common research using random people in the world.What you call as survey sites are the people who taking that responsibility on behalf of companies.
So what they do is registering people all over the world into thier sites and giving some forms which are including questions about products or services what companies request from them,And they for that too.Most of them are done by e mails.So many people trying to join a survey site and earn some money by taking some easy surveys.
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