Car Max: High prices with no wiggling or haggling. Limited finance options requiring high down payments. Too many overhead costs and mouths to feed. Vehicles purchased at auctions and quickly run through the shop to seal leaks and detail them. Mechanics in their shops are dealership rejects who smoke too much weed on lunch breaks. Company policies dictate EVERYTHING personnel do and canned responses to every question.
Buy your used cars from a mainstream new-car dealership off their trade-in lots. Go to a Lexus, Range Rover, Jaguar, Cadillac, Mercedes (et al) dealership and look at what the affluent types have traded in to get into one of the more expensive luxury vehicles. Affluent clients tend to keep MUCH better care of their vehicles than the average person. Cars/trucks traded in by folks who never have had a problem coming up with the cash to fix them, are the best vehicles to find. Period.
All great information, though it's fair to mention that often times, vehicles traded into high end dealerships are sold into the auction circuit, even if that dealer has a pre-owned lot. When I bought my Infiniti, I applied a similar school of thought to yours and looked around at high end dealerships for pre-owned inventory. Most of the dealerships I visited sold most of their trade-ins on the auction circuit, allowing relatively few (typically just the best of the best) to make it to the pre-owned lot. The result was a car lot filled with $25k+ rides. They were more than willing to haggle, though, as I managed to roll away with my G35 for $16,500 cash (5k under their sticker price).