Buying a new car is a real "psychological" game between the dealer and the buyer. When I first got out of the military, back in the late 60's, I took a job as a car salesman for about 4 months while I was sending out resumes, etc., waiting for a "real" job. THAT was an education. Every morning, we had a sales meeting where the sales manager would offer "tips" on how to "fleece the flock" of buyers. Then, when I landed my career job as a high end computer tech, I serviced some of the major auto plants and saw, first hand, how much it actually costs to build a car/truck.
The profit margins vary widely, depending upon the type of vehicle. The small econo-boxes, listing for under $20,000 have a slim profit margin....usually in the 2 to 5% range, whereas a loaded pickup truck can have a profit margin as high as 40%. A small Ford Focus, for example, listing at $17K, might only have a $500 markup, whereas a loaded Ford F350 Diesel, with a sticker price of over $70K might only represent an actual $40K in manufacturing and dealer costs.
A good rule of thumb, on an average family sedan with a sticker price of $30K, probably has a real manufacturing/dealer cost of about 25k, and allows the manufacturer/dealer a reasonable profit. A good point for negotiation on such a vehicle is to take the sticker price and subtract 20%, as the price you will be willing to pay. Anything more than that leaves a smile on the dealers face. Thanking the salesman for his time, and walking out, will invariably result in a call a day or two later with a far better price than they will give you during the heat of negotiations.
Insofar as a dealer taking your registration, etc., and making you come back to get it....I would Never visit that dealership again.