We should all be vary wary about the word FREE, as it is more often than not, incorrectly used. Probably the tag line ought to read, we will give you something in exchange for something else which is not of immediate monetry value. As the item offered as “free”, often is given in exchange for information of some type, even if the information is gathered seruptisiously.
We have just added Eukanuba to Wabbit, Free puppy food, in exchange for information about your dog and all your personal details including your date of birth.
Simply knowing there is a puppy at your home address has a good value, added facts like your age, the dogs age , breed and so on must be worth much more than a sample pack of dog food, one per household. Someone will have a monetry value to each piece of personal information freely given, there is that word free again.
We sometimes send out free chocolates, as a thank you to customers who have bought chocolates from us and had them sent to someone else, usually as a present. 
So what do we get back? We get a very happy customer, who not only has chosen our products to give away but has now been able to sample the same products given in the present. What value does a doubly happy customer have?