Answer:
He's been subjected to the foot-in-the-door phenomenon.
Explanation:
This technique is also abbreviated as FITD. It states that people are more likely to compyl to a larger request if they've already complied to a smaller one. This can be explained by the person's need to be consistent with their previous agreements.
The name is an anlogy to a salesman who keeps their foot on the door, so the customer now feels obliged to listen. As expected, this technique is often used in marketing.
