Markups are super annoying, but identify them quickly and call out the dealer ASAP when looking at new cars. Literally call them out, to their face, and say “No”. Don’t let them use pointless markups in price negotiations! What I do is find the average price of the car across multiple dealers, subtract all stupid markups, delete the cost of dealer added “upgrades” subtract a few thousand and work from there. There is not much wiggle room for brand new cars, so don’t expect to get a deal of the century. Used cars are a totally different beast, but you can basically ignore markups as well.
Provided that your local dealers aren’t affiliated in some way, play the long game and play them against each other in a mini-price war. Stupid markups will generally evaporate naturally in that case.
(LPT: Do not sign anything but the actual loan paperwork or contract to buy the car. This will piss off a sales person to no end, but they will get over it. I can go into details why, but I am already outside the scope of this thread.)