Nobody likes buying cars, but I kinda like it. I negotiate for my parents, siblings and a few friends.
First off - take a couple hours and do your homework. Know what you are looking for and how much is a "fair" price.
9 times out of 10, I have financing in place before I make a single call or email.
I only talk to the sales manager or used car sales manager. Not wasting time with the guys that have no authority or are just learning the game.
I am polite and do not use a demanding tone.
I keep my communications short and sweet. "I am interested in one of your vehicles (stock number) - I have financing in place ready to go.
I would offer you X amount - no more. I am ready to buy today. If you can not meet that price, I understand and will continue to search"
I also add that I do not have much if any time to come in and negotiate. Just get the car ready and my bank will call your bank and we can be done.
Believe it or not, most salesmen hate "the game" as well. I'll always add, you can sell me that car in 10 minutes and have the rest of that time to sell another car to another client. Most appreciate the time savings as well. Anytime they start with the song and dance, cut them off and tell them that you do not have the time.
You have to be realistic too. If you are buying a new car you can't expect to get 10 grand off a 30k car... Also watch the fees for paper work etc.
Most states have limits as to what can be legally charged. Those can be negotiated as well. Last time, they tried to charge me $300 for paperwork. I told them I understand that they can charge some, but since I did most of the legwork for them and saved them hours of negotiation I'd give $100 and that felt like too much. Of course they said no, and I told them that believe it or not, I would walk out for that difference.
Be upfront and curtious with the salesmen from the get go. Saves everyone time.