To buy for another. To take one's place in buying a product.
Side note: Most stores have a policy that forbids them
from letting a second-hand sale for certain items
Customer 1: I would like to buy a pack of Cigarettes please.
Cashier : Certainly, do you have your I.D. on you?
Customer 1: No I do not.
Cashier : I am sorry, then we cannot sell you the
Cigarettes. We need to see a valid I.D.
Customer 1 leave the store and in comes Customer 2
Customer 2: I'd like to buy that pack of Cigarettes for my
friend who just left.
Cashier : I'm sorry but I need to see your friends and
your I.D. before I can sell them to you. Our
policy forbids us to let a possible Second-hand sale
Customer 2: But I have my I.D.
Cashier : I'm sorry but your friend is the the one who
came in first to buy these and if he doesn't
have his I.D. I cannot sell these to either of
Customer 2: Fuck you man.