The mistake in gp is that a car buyer and a tenant are not in a zero sum negotiation. If you look solely at the car purchase a buy and seller are. But there is more to that -- there is the time spent shopping and the advertising to acquire a customer. The clock is constantly running on both of those. So it is a positive (or elimination of a negative) to complete a deal.

This is why it is easiest to negotiate when you don't actually need to.