Last year, I found three used avalons that were two years old at the toyota in south austin. Close to 40k miles. They were lease trade ins, all in great shape for a really good price. The salesman was trying to work in all the usual questions. I kept being vague. I ended up buying a honda so I didn't have to do the full wheel and deal thing with them.
So I'll give my used honda experience.
At the time I was considering nissan, honda and toyota. Carmax allowed me to test all the models I was interested in. and narrowed to a honda accord.
I did the background and learned the different trim levels for the years you are willing to buy. Identify which ones you are okay with and which ones are non starters. For me it was a 2-4 year old car with under 40k miles. I crossed off the two base models. I then used the sites available and got an idea of prices. That gave me a range of prices based on the trim and year.
I went to the howdy honda place in south austin (I live in pflugerville and work off lamar in austin) and asked what they had and their prices. I was fully prepared to leave if nothing was in range. I was going to have to drive by at least one other dealer on my way home so I wasn't going to be going out of my way. I already had a caravana listing that would work if they didn't have anything. I fully anticipated not buying a car. Then it happed. They had a model with less than 20k miles and their price was less than what I would have expected on KBB, they bought my truck for more than KBB. No haggling.
If I was going to leave a number with anyone, I wouldn't do it on the first visit. Tell them you'll be back when you have a better idea of what is available around town. If they push, flatly tell them no. The last time you shopped for a car, salesman pestered you long after you were done shopping and that's not okay. Get their card. Use their number/email to negotiate from home. If you get to negotiating, use a burner number via google voice and/or email that you can delete when you are done dealing.
As for the buying side, their salesman, err Finance Manager, tried to sell me a warranty "We do so many loans with your credit union, we have a warranty for cheaper than anyone else..."I told him "I was just sold on a car because it was reliable, are you telling me I am not buying a reliable car" and he started to respond and I cut him off. "No warranty. I want to leave"
Anyway, I have given up on getting the best deal of all time. But I have also given up on trying to get the perfect car/truck.