If you do favor to one person, will this person more likely comply to your request? Dennis Regan studied this question in 1971. The purpose was to validate:

• Subject is more likely to respond your request favorably if he likes you
• Subject is more likely to answer your request favorably if you just did him a favor

The experiment is complex.  As usually, it uses a confederate.   In a first phase, the confederates manipulates liking: becoming either pleasant or unpleasant (depending the way he answers a phone call).  Then, they have to participate to a common experiment.   Then, the confederate manipulates favor.  For positive favor, he offers a soda to the subject.  For no favor, he does not offer a soda.   For irrelevant favor, another person offers a soda both to the confederate and to the subject.

Then the experiment measures the compliance to a request.  Thus, the confederate proposes the subject to purchase some cheap raffle tickets.  The amount of purchased ticket is the metric.

The experiment measures also the liking by asking, among many other questions, to rate how the subject felt toward the confederate.

Following are the average purchased raffle tickets depending on the experimental conditions

The experiment shows that a favor increases the likelihood to comply with a request.  It seems that the Reciprocity principle applies here.  The normative pressure to return the favor is stronger than the attitude.

Of course, good social engineers use this trick.

D.T. Regan, “Effects of a favor and liking on compliance,” Journal of Experimental Social Psychology, vol. 7, Nov. 1971, pp. 627–639.