Is it true that you have to mark a best response before getting paid for...?

I think you have probably heard wrong. When you post a discussion and somebody responds to it, then you get a point and you will also receive payment for it. I have noticed that there are quite a few people who do mark a best response and I don't think they would do this if they thought they weren't going to be paid. It is however nice to mark a best response and I think it encourages people to respond to your discussions.