During a downtime in my work life, I was essentially forced into a situation where I had no other choice but to spend a year in car sales. It was extremely stressful, and primarily because I was having to close deals to make a sustainable salary. And I did very well that year, but the crap that I saw going on there... and then left there and then went to work for another dealership, thinking it was different somewhere else. But it wasn't. Not back then anyway.
Today it's a lot different. There are thousands of more dealerships and it's a lot more competitive. And although most of us still hold the auto sales industry in contempt with regard to the old (earned) reputation of being aggressive, ripoff artists, a lot of that has changed over the years as well. Not all dealerships, mind you... but you now know which ones are good versus the ones to avoid. Also... there's a huge market now for used automobiles, because not everyone can afford a $600/month car payment. As a result, there's a little more to be gained from a trade-in... but also keeping in mind that if you're expecting to get the best price possible buying new - don't expect to get more than listed blue-book for whatever make/model you're trading in, unless you just so happen to be working with a dealership manager who values volume and there might be added incentives going on.
Once a vehicle gets over 175k miles (unless it's a make/model with an excellent history of reliability) you're better off either selling the vehicle on your own or just keeping it as a backup car. You're not going to get an offer from a dealership that is more than the vehicle is worth to you, providing that it's still running well.
I've been fortunate. I found an auto mechanic who I play golf with on occasion, and he's extremely reliable and knowledgeable, and although he's usually 10-14 days out with new work orders (being busy in that particular business usually means they're both economical and very good at what they do) having that golf-friendship aspect has quite often gotten my vehicle in for service a lot sooner. And he always gives me a break on the labor... case in point - I had a timing belt needing to be replaced on a Honda several years ago, the local dealership quoted me over $900 to replace it. He did the job for $350. That Christmas - I mailed him 4 free guest passes at the club where he and I would play on occasion. Finding a good mechanic isn't easy, but when you do find one - you'd do well to keep him!
And good car salesmen are the same really. When you find one that you can trust, one who is willing to negotiate a fair price and appreciates your repeat business and your word-of-mouth advertising - you'd do well to stay with that guy, because he's usually not going to compromise your loyalty for what amounts to a couple hundred dollars in the end.
All of these things help keep automobile expenses less expensive. But finding people you can trust - that's where it all starts.