In terms of wriggle room, it depends. Each car manufacturer is different when it comes to new cars. In many cases it’s only a 5% markup from invoice price (high end luxury cars tend to have more of a markup – in the 7% – 10% range). BUT, manufacturers often give incentives and rebates to the dealerships, making their profit higher.
Used cars are a different story as they tend to get marked down the longer they sit on the lot. They need to keep fresh inventory. If a car has been sitting on the lot for a VERY long time, you’ll find that they may even sell it for even money if you hit them at the right time (just so they don’t have to bring it back to the auction).
Wholesale dealerships have a VERY small markup, sometimes only a few hundred dollars over what they paid for it.