dryspot,
1. If you are guessing at an answer you deserve to be disqualified. The survey companies are looking for a particular demographic of honest people. Even if you are honest all the way down the line you will probably get disqualified 90% of the time. Every survey, every day is looking for a totally different set of people for answers depending upon who is sponsoring that particular survey and what they are trying to find out.
Also, Surveys are rarely national or worldwide in their scope. For example, today's survey may be Walgreens trying to find out where Latinos in Miami buy their toothpaste. The next survey may be Verizon Wireless trying to find out how many black police officers in California play Angry Birds on their cell phones. Both companies hired the same survey company to conduct the survey. Odds are pretty good that the average person on WGT (or anywhere, for that matter) is not going to qualify for or complete either one.
2. There is a better way to earn credits. Buy them.