lol yeah, people figured out that people who fit a certain profile would get more surveys (such as women in a certain age) so people would pretend to be different ages, genders, etc. to get more surveys. I think they eventually screw up and answer something wrong.
Google also sends out fake places. "Have you recently visited D-Bag's Water Adventure?" "Mmmm survey money" *clicks yes* "THERE AIN'T NO MUTHAFUCKIN DBAGS WATER ADVENTURE YOU SON OF A BITCH, CUT THAT SHIT OUT"