Albeit it is annoying when dealing with the cliche and stereotypical car salesman, I would either accept what he is offering you and be happy or move on to a different dealership. Its unfortunate this instance came up, and we all know at some time this has happened to us where there was some small print we had to read or something we had to look at closely. I do not feel it justifiable to do anything malicious or brash to the salesperson though, you would be just showing how rude and unappreciative a customer can be. It could have been a honest mistake on his part or someone else's, or someone else's wrong doing, yet he will catch the blame for it. Thats like blaming a waiter for the cook's mistake, not really all that fair. Coming from years of customer service, sales and managerial experience, the nicer you are about the situation, the easier and better the outcome will be. I'm by no means telling you to "bend over", however I think being reserved and mild-mannered about the situation will allow you to make the mistake of trading in that incredibly awesome 370 for that mustang.
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