Nothing like the word Free to make you take notice at a supermarket. But of course there is always a catch since I have to buy at least one 16 oz. package for $3.99. So what I'm really paying for my free box of strawberries is $2.00! Now if I'm in the market for more than one package I might consider paying $2.00 per package. But since for me they go bad pretty quickly and I'll never finish the second box before it does goes bad, that really means I'm paying $3.99 for the box I actually eat! Wouldn't it be just plain old easier and more honest to leave the word "free" out if the sign read:
Get your students to find examples of this and to write the manager of a store that pulls this nonsense and see how the company tries to justify this deception.