Not true. As recently the 90s expensive niche gear like a pro audio or video stuff was almost always subject to price negotiation, especially if you were a repeat customer or indicated an interest in possibly purchasing other stuff. It still is to some extent.

In general the more knowledgeable the dealership/salespeople, the more likely negotiation is possible, especially if you present as a knowledgeable customer so that neither of you are wasting each others' time.

I guess I was a kid back then, but I don’t remember any of the adults I hung around haggling in stores like circuit city, and my family are immigrants from a country where you haggle over vegetables.

As far as I understood, it wasn’t in the interest of the big retailers to spend time haggling with individuals.

Exactly! And the same fate is waiting for "thanks for the time you just wasted, but I'd rather check out the competition next door some more".

For most people, this has already happened. It's just not as visible as haggle/no haggle (even to the people doing/not doing themselves)

Sales needs to adjust to the new reality. Recognize that people have options and other sources of information and focus on answering their actual questions instead of trying to sell them on something.

If I walk into a car dealership it's because I need specific information not available online, even if it's just to see the car in person.

What I don't need is a whole sales pitch. That's wasting my time and the salesman's.