@Bhutan - I just fill out the form and be done with it. I think that the best sampling methods in research involve offering a survey along with follow up questions like many market research companies do.
When they call you they often verify if the answers that you initially gave were correct and if the answers do match then they offer you an opportunity to join a focus group.
They are very selective because you really have to match the customer’s demographics in order to give valuable feedback. I was involved in a focus group and it was really a lot of fun.
I was asked questions about my experiences with a particular retailer and its competitors. It was about two hours and I think I was paid like $150.
I did notice a substantial difference in the customer service level in this particular retailer so maybe they really listened to our suggestions.