This article discusses the different tactics marketers (as well as, the general population) use to persuade. Through several new experiments, researcher Dariusz Dolinski of the Warsaw School of Social Sciences and Humanities in Poland found that when people were first presented with a highly unusual question initially, they will be more inclined to comply with the request that follows.
His methods of determining this information was through experimental research. One group would get a routine marketing survey, while another group was asked an unusual request. Those who were asked an unusual request were more inclined to accept a different request later on. From the sounds of it, the participants were not informed beforehand that they were part of an experiment, but to do so would likely affect the outcome of the study. Although this may be considered an ethical issue in some people's perspectives, I think it is morally sound as long as they are told at some point during the study - no one is being hurt by no knowing initially, but it is necessary that they be told.