Answer:
Foot-in-door technique
Explanation:
The foot-in-door technique is used by many people in society. This technique is meant to when a person does a small request to a person and that person replies in yes, the other person then makes a big request. It is done because people thinking that if you make other people agree at small request then you can make them agree with them at a bigger request.
These techniques are used by the salesperson. Salesperson used this technique so that more people can buy their products. Many people used their knowledge so they could not be persuaded by other people to buy a product that does not need it.
Thus in the above technique, Bart friends used the foot-in-door technique to make Bart agree at bigger requests.