A lot of services will offer a free trials, which is an example of reciprocity. Reciprocity is when a friendly or positive action by someone, or in this case by a company is more likely to result in a positive response from the individual, or alternatively a negative action is more likely to elicit a negative response.
Reciprocity was shown by Regan (1971), who told his subjects that they were taking part in an “art appreciation” experiment with a partner who was a confederate of Regan. The confederate bought the participant soft drink. After the experiment, the confederate then asked the participant to buy raffle tickets, participants in the condition in which they had been bought a drink, bought more raffle tickets than participants who had not be bought a drink.
In cases of having a free trial the customer may be more likely to then go on and pay for the service than if the trial had not been given because of the positive nature of being given something for free, or maybe just because they forgot to cancel the service.
Regan, D. T. (1971). Effects of a favor and liking on compliance. Journal of Experimental Social Psychology, 7(6), 627-639.