Sorry, that's not true at all. There's often A LOT of wiggle room.
Insider Tip: The internet desk is usually separate from the floor desk at your average dealership. When you know exactly which car you want to buy, negotiate through the internet desk only at several dealerships. But be prepared to walk if they try to pull a bait & switch when you show up to purchase.
The problem with your insider tip is that everyone, dealer included knows about it. I hate when people say be prepared to walk when most of us don’t have a million dealerships to visit. Sure if you’re in Southern California you can visit 6 Honda dealers and waste 1-2 days. You’ll get the quoted price and then they’ll try to stick you the next time you come in. Consumer is at a huge disadvantage here because dealers know they have limited time. It’s no secret dealers make you wait forever so you grow impatient and agree to their bullshit. Some of us don’t want to deal with that kind of crap.