Even if this weren't the case, if you're ripped off by a used car salesman you will tell every single person you know that they're a snake.
Even if you don't do that, there are arbitration courts you can take them to to both waste their time and force a refund (VCAT where I am, I'm sure there's something similar overseas).
I really don't think it's in a used car salesman's best interests to lie and swindle.
A collaborative approach is a lot more like when you ask you're knowledgeable friend "what kind of bike should I buy?" and they ask you about your needs, goals, and budget then guide you towards specific options. They're helping you make a purchase, without pressuring you into something that's not useful to you.
I get what you mean now. As someone who "does sales" a fair amount in my work (owner of a second-hand video games business) the adversarial stuff is actually really frustrating.
I always try to give the customers the same advice I'd give a friend or family, even "downselling" them from a $100 purchase to a $25 repair if that would be more suitable, yet still so many people are adversarial and distrustful.
From my experience, this distrust hurts (non-expert) consumers even more than it hurts the businesses. Ideally, you'd have an honest salesman pointing out the pros and cons of all the different products so that the consumer can make an informed choice. Maybe that product that costs $50 will last for 20 years of continuous use, whereas the $30 version will break after 18 months.
Instead, because salesmen can't be trusted, they rely on their own instincts and buy products whose prices are completely uncorrelated with quality.
At work you have or done have a job or even revenue if the only thing employer and employees are doing is trying to throw wrenches into the machinery to get the upper hand.
In an unending game of the prisoner's dilemma, either you all win or you all lose.
Now obviously all other things being equal, I'd rather pay less money (or charge more money)
But in most cases, neither the seller nor the buyer operating in good faith will really try to squeeze the other because losing a multi-hundred-thousand (or even million+) deal by being too anal about $1000 is in neither one's interest.
If a seller got very "adversarial" most buyers would say "fuck you, I'll keep looking."