I'm a Bad Negotiator

My 2.5 year old son is a very picky eater. So being a good economist I bribe him to eat healthy foods. Unfortunately, he seems to have worked out all too favorable terms of trade. He has successfully negotiated to get one cookie for every grape he eats. And at these terms he still acts as if he is being treated unfairly. I sometimes wonder if he is faking his finickiness just to get bribes.