A movie theater in Santa Monica, California, advertises that it will give you a free box of popcorn if you donate $2 to charity.
The usual gimmick at movies is that the profits from sale of popcorn and other refreshments go to some charity. I have a charitable motive, so I, and no doubt many others, are more likely to buy the $5.75 small box of popcorn knowing the profits will go to charity. But I’m uncertain how much of the $5.75 is profit.
The $2 cost of a box of popcorn is a very good deal — a tremendous incentive to move down the demand curve for popcorn, especially knowing that the entire $2 goes to charity. The consumer does well by doing good — and it is great publicity for the theater.