This is not all true. One thing that people who do not work in the industry in some fashion do not know (I work at a bank and know very well how car dealerships work because several finance their dealer floor plan through us) is car dealerships do not expect to make a lot of money from profit margins based on sale price compared to invoice of new cars...This is part of the system and is misleading and a farce. Sure, this is 'technically' what the books say the dealerships get the cars for, but what most people do not know is the dealerships get significant kickbacks from the manufacturer for moving product as quickly as possible, and believe me they make plenty of money by selling a new car even if it below invoice. Every car they sell, even if they sell it below invoice, they make money by kickbacks from the manufacturer. That is how a dealer floor plan works. They also get a percentage of the interest when you finance a car...Most people don't realize this. Finally, they really make their money from the service department and parts. This is really what keeps dealerships profitable and they know it. It's all about moving as much product and keeping you coming back to them for service and parts.
Finally, when talking about trade-ins and it being a rip off, you are completely omitting the fact that you do not have to pay any sales tax on your trade in, which you otherwise would. If you are like me and traded a car valued at $8,000+, this is a significant savings. You take this and the fact that you don't have to worry about any of the hassle of a private sell or liability (the person who buys your car suing you if something goes wrong), trading in is not always a bad thing.
I apologize if this post comes across harshly, most people do not know how car dealerships really work and how they make money, and I just want to clarify how it does in reality