I have had five cars in my life – a shitbox in college, a used Jetta GLI, a Ford Explorer XLT, a Volvo S60R, and a Mercedes E-Wagon.
Setting aside the college beater, the Jetta was super fun but after four years the transmission and AC failed. I replaced the starter four times in six years and the alternator twice. There was an electrical system problem that took two VW service departments 8 months and two batteries to identify and fix. Thankfully it was really easy to work on, so I did most of the work myself (except the tranny and the mystery short problem).
The Explorer was exactly what I wanted when I bought it. I drove it cross country and back eight times. When I sold it after eleven years, it had 288000 miles on it. The 02 sensors were poorly engineered, so I had to replace them at least once a year. But the brakes were the worst. They were the same discs and pads as the Taurus, but on a vehicle almost three times heavier. I don't remember how many times I did the brakes.
The Volvo was also exactly what I wanted. The driver seat was the most comfortable I have ever been in and I'm 6'6". But mine was from the era when Ford owned Volvo, and the quality was not Volvo standard. The fit and finish were awful. The cooling system was total crap and the automatic transmission was cheaply designed. The best part of the Volvo was the Yamaha inline 5 cylinder engine.
Finally I graduated to my lifelong dream car – a Mercedes station wagon. At 6+ years, I have not had to repair or replace anything except consumables (tires, oil, filters, brake pads, etc.). When I had the brakes done at 80K miles, the discs looked brand new. I firmly believe that you get what you pay for.
As for advice: find 2-3 cars that you would be perfectly happy with. Research them exhaustively. Watch for incentives (manufacturer, financing, dealer) religiously. Keep an eye on their inventory online. When you decide that you need to purchase, email the Internet Sales or Fleet Sales person. Tell him/her which exact vehicle you are interested in buying and ask what the bottom line, out the door price will be if you come in tomorrow.
I bought my last two cars using this strategy and have been extremely happy with the process. I do not like the negotiation, the "let me check with my manager," or the "how much do you want to spend each month?" crap. Come in pre-approved for a certain amount from your bank or credit union. Most times, the dealership's finance department can match or beat the financing you already have, but in case they cannot, you have your backstop. Sales floor people might give you the stink eye or try to claim that they gave you a test drive and deserve a cut of the commission. (This happened at both Volvo and Mercedes.)
Good luck!
PS: It is impossible to know how much a dealer paid for a used car or how much, if anything, they put into it before selling it. I loathe being taken advantage of and this lack of knowledge prevents me from being comfortable buying a used car. The Jetta was the only used car I bought. But I keep cars for 10+ years, so I not worry much about depreciation.