Answering the question of what is fair? in negotiation is very difficult. Think about that case. A shop’s owner had to leave for little time so he asked a friend to cover for him. While the owner was gone, a kid came in and paid $5 for a rare card that actually was priced at $500. The friend had wrongly assumed that there was a decimal point. When the owner learned of the mistake and went to the boy's home, the father refused to return the card. "A deal is a deal", he said.
What is interesting is how people reached to conclusion. Some say that the father's attitude is senseless, he failed to take into account how his reputation will suffer. I don't see that as an ethical argument. It's really just a different calculation of personal costs and benefits. Other people see the situation in moral terms and requested we should treat others as we’d like them to treat us. Others emphasize relational factors, that a parent should set example for a child, or the matter of taking advantage of an inexperienced seller.
Regarding people as individual materialist is a valid point of view, but it isn't the only one. For others, meaning in life is created by how we relate to one another. They believe that attaching a price to integrity and loyalty is fundamentally to debase it.
So what makes a great, ethical negotiator?
Prudence is critical to maintaining ethical standards. People get into trouble when they make hasty decisions. Before you go to the bargaining table, you should anticipate tough questions, and you should have an answer that doesn't compromise your values. Planning ahead is a lot easier than constructing intricate excuses for your behaviour.