I gave away a very nice rooster I had for sale at a show to a young 4H girl that I know, making sure that she OKed it with her mom. I know and like them. She immediately turned around and gave it to her friend. This made me angry--it was a gift to her, and turning around and immediately giving it to someone else was very inappropriate--if that girl really wanted it, she could have paid me. But mostly it was the principle of it--if I give someone a Christmas gift, I do not expect that they will immediately give it to someone else.
Kids learn by doing, and haggling is a part of it, although I do think there is a difference between haggling with a shy 8 year old and a determined 15 year old. Although sometimes it is the determined 8 year old and the shy 15.