I have to say. The whole “walk out if the deal changes” line is absolutely true. I did that when I was recently shopping for a used car and the dealer froze in his chair.
I walked about 500 feet across the parking lot to my car, got in, and started to drive away when I shit you not, the dealer ran all the way over to me and was knocking on my window. I rolled it down and said yes? He said well we can do X for this vehicle now. I said, “Well I think I need to continue shopping because I can’t do X. You have my phone number. If you can do a better deal, please call me.” Then I drove off.
Even though I didn’t take that car, I felt so great afterward. I’m not the best negotiator but my willingness to walk from the deal really paid off.