Answer:
Social proof
Step-by-step explanation:
Social proof to the phenomenon where people copy the actions of other people or peers to imitate their behavior in a social environment.
It usually happens when people don't know what is the right way to act in social situation and therefore they assume that the other people have more knowledge than them about the situation.
In the example, Ben notices that all of his peers have name brand shoes, he doesn't really knows much about the theme so he assumes that the others have more knowledge than him and that their shoes have a better quality than his. Because of social proof, he ends up buying name brand shoes for himself.