Gifts are very useful to con men. Gifts create a feeling of debt, an itchy anxiety that the recipient is eager to be rid of by repaying. So eager, in fact, that people will often overpay just to be relieved of it. A single spontaneously given cup of coffee can make a person feel obligated to sit through a lecture on a religion they don't care about. The gift of a tiny, wilted flower can make the recipient give to a charity they dislike. Gifts place such a heavy burden that even throwing away the gift doesn't remove the debt. Even if you hate coffee, even if you didn't want that flower, once you take it, you want to give something back. Most of all, you want to dismiss obligation.