Excuse me, are you the kind of person who will get a lot of bonuses if you sell it?

If so:

1, you can see what the students in that school like. For example, they like game cards. You can say that if you buy milk, you will get a game card. If I were you, I would definitely buy it ~

2. If the accountant is responsible for the milk at school, you can give him some money or something.

If not:

1. If they don't want to, make friends with them after they refuse you (provided they have a good attitude) and ask them to introduce you to some "customers".

You try it first. I have little experience. When I have a good idea, I will tell you to come on.