Your examples are flawed because you are coming up with a number out of your ass. The idea is to gauge the used car value and then make an offer lower than that. In the first case, you wouldn't offer $10,000, you'd offer $3,800.
Funny enough, this is the method my Dad uses to buy cars and it works almost every time. But it requires that you understand the lowest number the guy can go without taking a hit. Once you know that number, go a little lower and tell him that the day he can sell at that number, he has your business. After my dad has done the research, he explicitly tells them they do not need to sell him the car as a salesman - he knows what he wants and for how much. The day the salesman is ready to sell for the amount specified, he should call my dad. They do. Every single time.
>But it requires that you understand the lowest number the guy can go without taking a hit.
I don't give a damn if he takes a hit or not. His profitability is his problem, not mine. Ideally, he takes a loss on the car he sells me because that sale pushes him over some target that actually works for him. Only he knows his position explicitly. I can never know this. Assuming I can is putting me in a loser's position.
Generally, if a car salesman isn't pissed off at you following the sale, you are getting ripped off. I hate to tell you this, but it is true. If the car salesman is "happy" to sell to your dad, it's probably because he's an easy sell. That's not negotiation.
The first case is only an example, but your $3800 offer is pretty close to my example where you offer $2000. The error you're making is that $4500 is some sort of set in stone value. It isn't. The car might in fact be worth more than $10K to you, and less than $1K to the dealership.
The art of negotiation is the act of getting the car for the lowest possible price, regardless of its worth to you or the seller.
Generally, if a car salesman isn't pissed off at you following the sale, you are getting ripped off.
Yep, they are usually pretty pissed at my Dad.
Ideally, he takes a loss on the car he sells me
He is not really taking a loss if he's meeting a target that net makes him a profit(in some manner). You seem to argue that you can't extract such information. I'm arguing that you can.
The point is he might be making a loss to the business for some other goal (e.g. making a quarterly number that his boss will reward him for, costing the business even more), so making assumptions based on the value of the expected average market value of the car has a decent chance of setting the value higher than the value of the car to that salesman at that point in time.
Funny enough, this is the method my Dad uses to buy cars and it works almost every time. But it requires that you understand the lowest number the guy can go without taking a hit. Once you know that number, go a little lower and tell him that the day he can sell at that number, he has your business. After my dad has done the research, he explicitly tells them they do not need to sell him the car as a salesman - he knows what he wants and for how much. The day the salesman is ready to sell for the amount specified, he should call my dad. They do. Every single time.