POAers - don't let Ted's on-topic and thoughtful reply distract you from my needs!
Fine, here's my advice then.
Wonderful timing... I'm about to buy a nearly-new car. Time for POA to share some wisdom!
I've owned 42 cars, but just four cost more than $10K (and several were race cars). Haven't bought a car from a dealer since 1990.
Stepping up to a nice grown-up car that feels painfully boring. Looking at 2014-2017 Mazda6 sedans. Red or Blue. No kitchen appliance colors! Grand Touring if I get an automatic, or Touring if I stay stick-shift.
Found a few. Major, major sticker shock. Wow. All at dealers, mostly Mazda dealers with trade-ins or lease returns. One 'credit union' dealer. All 50+ miles away, so won't get serviced there. Two are "Certified Pre Owned" with an attractive warranty. Is this worth anything?
Gonna test drive three this week. Ideally, I'll arrange for a 48-hour test drive (and willing to put a deposit down). Go immediately to my trusted Mazda mechanic.
How much can I lowball them? Ten percent? Twenty percent? There's a price where they say "No." I want to be $1 more. Paying cash.
How can I find out what they're really willing to accept, and do it reasonably efficiently?
Thanks for the POA wisdom. PMs/Emails welcome.
I've owned around 40-some cars myself.
First piece of advice, which I'm sure you well know: If you think the car will be boring now, then it will be very boring later. So buy something fun! I'll sell you my 2003 Mercedes E55 AMG. That thing's a blast! Although the automatic is starting to get on my nerves, I hate anything without a clutch and have been thinking about buying a Kenworth. Also selling a pretty mint 2003 Avalanche and a 2000 F-250, but you don't want the F-250, it has a dead cylinder. Now with that out of the way...
I personally don't care much about "Certified Pre-Owned." Basically a marketing gimmick to sell a used car for more money. Usually has more of a warranty involved, so you need to look at the numbers to see what you get. I also personally don't much care for warranties on newer vehicles since, well, they usually don't need them anyway. I believe those 6s all were good from a reliability perspective.
I would try to avoid a dealer if possible. You will pay an upcharge, and they will also try to sell you on financing. Paying cash often isn't an incentive because many dealers make a bunch of money off of financing. If you can pay cash, though, that makes it easier to negotiate with a private seller.
In terms of the amount you can low-ball them, again it depends on the dealer, their mentality, and how they priced it. A couple weeks back I went to go look at a used Dodge at a dealership. I ended up looking at two. On one they would come down $500, on the other one they wouldn't come down a dime. They kept on saying "The bank will loan you twice as much as we're asking on this vehicle, so that's what it's worth." Of course, they were full of crap. Both were priced above what they were worth. I've never run into that before. By comparison, I managed to get my wife's Excursion that we just bought recently for 15% less than asking price, which wasn't a bad price to begin with. One big difference is we bought the Excursion from a used car dealer, and these Dodges were used trucks on a Chevy dealer's lot.
So, I'd look for private seller. Or if you go dealer, go with a used car dealer. I've actually had much better luck with them.