As you complete more surveys, providers will attempt to match you to surveys that you have a better chance of qualifying for. Some of those may be higher paying, but the surveys you see can also be influenced by your demographics. It's always good to have a higher quality score, because a lower score could limit the number of surveys you see.
Basically, a good quality surveys gets you +1 and if they don't like a survey or it gets rejected it's -1 and the goal is to stay above 100. If people take time and provide quality responses their score will go up over time. Other than that, they do not share specifics. The important thing though, is to just continue providing quality answers.