I tried to find an example of the promotion online, but couldn't. I'm not sure what the specific mechanics were, and it may have been an unadverised deal.
So, family appears at strore, is unexpectedly gifted a gallon of ice cream, and finds they have to head home so as not to "waste" it. (What is actually being wasted is the comparison-shopping opportunity.)
Hrm... Maybe this was on an economics podcast / programme ... possibly Freakonomics. I'll see if I can't turn it up.
