I agree with your personal experience, and I also dislike such methods. That said, I'm reminded of what I recently read in "Getting to Yes", which commented on underhand tactics. While not recommending them (and refraining from opinionating on morals), the book pointed out some things to consider; particularly:
- whether or not the other side is someone you'll want to maintain a longer-term relationship with
- how use of such methods affects your reputation as a negotiator
Good considerations that shed light on why your experience with a new car salesman (representing a car manufacturer that is vying for your loyalty) can be so different from a salesman on a used car lot.
See also those late night infomercials that pack as many "parlor tricks" as they can into an ad, for a product from a fly-by-night company that you don't even know the name of.
- whether or not the other side is someone you'll want to maintain a longer-term relationship with
- how use of such methods affects your reputation as a negotiator