According to one of the moderators
They have a custom proprietary method of serving up users ads based on their quality score. This system rotates users ads randomly on unawarded questions with those who have a higher quality score having their ads shown more often then those with a lower score.
Try this thread
http://www.webanswers.com/webanswers-support/how-much-have-you-made-on -webanswers-com-75e314






