I too am amazed that car and matress salesmen continue to be so sleezy, especially in the Internet age where everyone can do extensive research at home before they ever interact with a dealer.
Personally, I feel comfortable bargaining, but as a starting point, I see what the starting price is at Costco. If the out the door price isn’t as good as theirs, then I can stop right there. Next step is to remove as many factors from the bargaining equation as possible. Sell the old car first if at all possible. Advertise it on Cars.com or similar service, and get a quote from Carmax, which is usually good for 7 days anyway. Now contact a credit union and get rates and quotes so you have a backup for financing in case the dealer tries to screw you on that. Sometimes the dealer rate is better and sometimes not.
Research the car you want in the color you want, and with the options you want. Now determine your flexibility on those colors/options. Call around and find out which dealers have what cars. Sometimes this is not always close by. For example, my current car is an Infiniti and I live in San Diego. The model I wanted in the color and options I wanted was rare. I think there were five in the whole city. Meanwhile, if I was willing to go to LA, one dealer alone had 20 of them, and most others had six or more. So, I made a day of it, had my wife drive me, and spent the entire day running dealers through the ringer.
It took about four hours and I visited three separate dealers, but I ultimately got it for $700 less than Costco, and I got it from the dealer who had 20 of them. I warned the first two dealers who jerked me around that if I sensed I was being jerked around I would walk away. Sure enough, they did, and I walked away. Both attempted to stop me and I told them they were too late. When I walked into the second dealership, I told them I had just come from the first dealership and had left for the following reasons… Then when I went to the third dealership, I let them know I had left two other dealerships for the following reasons… This made the third dealership take me very seriously. Once there, the whole transaction took less than 45 minutes. I ended up using their financing which was better than the terms the credit union gave me, and I read the paperwork twice to make sure there was no fishiness. I also told them that I considered this sale final and that any attempt on their part to pull some post deal shenanigans with extra charges would result in me immediately returning the car and demanding a full refund, and bringing them to court for any money they didn’t pay me due to any kind of “wear and tear or depreciation”. I got assurances from all parties involved everything was kosher and didn’t have a problem with them.
I accept the fact I’ll be unhappy dealing with them and prepare to do combat with them right from the start. I always give them the option to not be douchebags and let them know immediately when they have been and why in an effort to change the system, but so far, the world works the same way it always has