I don't mind a bit of haggle and I don't mind having to work through a bit of salesmanship, trying to upsell you, etc... What I can't stand is outright dishonesty.
There was a car a few years back I had seen online with a price I was willing to be near. The salesman kept saying the price I wanted wasn't even possible. I knew that the car was listed online at only 1000 more than what I was offering and so at most I'd have to come up to the 1000 except they wouldn't take that either. I told the guy that it was online at a different price than they were saying so he said let's go back to his desk and look. As I walked over, I pulled it up on my phone. He walks back to talk to his manager while we sit at his desk and I start telling my wife how I've got the car pulled up on the phone with the price I'm willing to pay.
He comes back and pulls up the site on his computer which shows a different price than my phone, so I turn my phone to show him that this is what they've advertised and the most I'm willing to pay. He says "I have some bad eyesight" and asks to hold my phone where he (accidentally) closes the browser. When I open it back up, lo and behold the price has changed from what it just was. I cursed the salesman out and walked out saying I'd never shop at an unethical dealership again.
Sure enough I get back to my office an hour or so later and pull the car up and it's once again listed at the lower price. I open my phone which still has the higher price listed, click refresh, and it changes back to the lower price. I'm absolutely certain that they went back to their office and changed the price online while I was there and then changed it back later.