I just wanted to chime in and say that as car dealerships go, I had a pretty good experience at Bommarito Cadillac in St. Peters, MO. I purchased a used 2011 CTS Coupe from Roger (who has apparently been selling Cadillacs for close to 50 years now, including once owning his own dealership down in Rolla), and he seemed to be honest with me and straightforward. The finance manager was friendly as well, and found me a loan with a good interest rate, on the first go-round. (I've found in the past, the finance office is where some dealerships try to make their money off of you, after you've fought and haggled to get the price you wanted. They'll add points onto your interest rate, claiming that's the best they can get you, or tell you you're only approved with one of the lenders they have arrangements with, so they get some kind of kick-back for working the deal.)
I haven't used them yet for any service, so can't comment on that -- but I do know their website makes it fairly convenient to schedule service appointments online and they send you email reminders when maintenance is due (with video messages, even!). Their dealership was pretty torn up when I was there, because they're in the middle of a total remodel. But if the neighboring Bommarito dealerships are any indicator, they'll have a top-notch facility when they're done -- complete with such things as a play-room for the kids while you're waiting.
Bommarito likes to offer their "Motor Trend Certified" warranties on their used vehicles, which I have some experience with and would say isn't too bad either. They throw in a "key care" package so if you lose a key or key-fob for your vehicle, you can get it replaced for free, and they have a "concierge" service they sign you up for too. (You call a toll-free number and you have X number of free minutes of usage thrown in with your vehicle purchase. You can call and ask about basically anything, from directions to a place to answers to homework, to a hotel or restaurant review/rating.) They give you dent repair coverage as well, but beware; this one is largely worthless because in the fine print, it says they will only pop out a dent if no paint damage is noted. It's not too often someone hits your car with a grocery cart or something like that and it dents the panel, but doesn't even scratch the paint.