Tesla just formalizes this by forbidding negotiation. Some people like that. But historically people like to negotiate on big purchases. It's a game, how close to invoice can you get, etc. Can't really have it both ways.
And frankly, most people like to pick from inventory, too, and have options. Tesla doesn't carry inventory nor do they really have much in the way of options. They're catering to a niche. People who are okay with a limited selection and are willing to wait.
Buy a Tesla.
Don't just go make Elon richer.
Every dealership I've been to will nod their head then precede to upsell you in F&I. They'll make sure you don't actually get to F&I until you've been their for 5 hours where you're so tired, hungry, and agitated you just want to gtfo with your car. That's not to mention todays market where every dealer acts like and prices like its a privilege to be able to pay them $50,000+ for a vehicle.
(setting aside the pandemic)
you always want to do your research before ever going to a dealer, any dealer. after that you go and see the car + test drive it.
after that you talk $$$. if you drag this process for more than 30-40 min or try stupid stuff, as a customer I will get up and walk. Also for my last car the dealer had a guy that was assigned specifically for internet sales and I actually saw the car in person + worked out all the details through email.
again, as a customer (minus the pandemic shiftshow which will eventually die down) you have the power to decide what is and what is not acceptable.
In this car market they’d be crazy to give up a car without upselling, given manufacturers’ prohibitions on raising prices.
I don't think you have to buy a Muskmobile to avoid rapacious dealers.