Dealers always try to make money on every deal, and the ones still in business make enough on most deals to cover the ones that cost them money. The successful dealers not only make enough to cover the bad deals, they make enough to make a profit. The really successful ones not only make a profit, they have customers advertising for them and customers returning to buy from them again.
We bought our mpg from a small, local dealer. We probably could have saved a few hundred dollars by buying from some larger, distant dealer, but then we wouldn't have had the offer of someone coming out to our place to help with a problem.
The best deal is when both parties come away feeling good about the deal. If the dealer didn't make much on your coach, you may find yourself at the end of the service line, waiting for parts, or made to jump through many extra hoops just to get some warranty work done.
The last time I was car shopping I found a vehicle I liked, got the KBB trade-in price, and figured a purchase price that would let the dealer make some money but was considerably less than what he was asking. I drove the car, liked it, and said I didn't have time to play games. Here is my price - take it or leave it. They came back with a counter offer, I put on my hat and coat, and walked out the door. The salesman just stood there with his mouth open.