I bought an Audi off lease last year. It's still under warranty, free maintenance (until 80k km), low mileage (37k km), fully loaded with options, and I saved $20k vs a new one.

CPO cars have a warranty, which sharply limits your downside risk. Buying a used car from a manufacturer is a much better deal than buying it from a third party.

Obviously, cars rarely fall apart as you drive them off the lot. Yes, there could be unexpected expensive repairs. But there's basically no realistic scenario in which you're going to be out the entire $35k.

I understand that you're exaggerating for effect, but it's this kind of thinking that convinces people to purchase expensive warranties that aren't (statistically) worth the price.

Generally not as nice as CPO, but it's something.

It's not. The parent doesn't appear to understand the used car market in the US. Most people are not buying their used cars for $6,000 off of craigslist, that's a good way to end up with a pile of junk. It's a bad idea to buy a mid-value or higher used car outside the CPO or remaining original warranty programs if you can help it, ideally from a dealer.

Tens of millions of people. It depends entirely on what you're buying. For example if you want to buy a certified pre-owned vehicle, you're frequently going to buy it off the lot from a dealership. The CPO programs from the major manufacturers are typically excellent. If you're buying a nice used car, with relatively low miles & a recent model year, it's more often dumb to go any other way than a reputable dealer + CPO.

If I had a used car worth 20K still in a maintenance window I wouldn't sell it on Craigslist. Autotrader if I wanted to private-party to max my upside, dealer if I was lazy.

Your 20k used car is 2-3 years old and coming off lease, or the same car as a trade in. The dealer will put it on the lot with a "just off trade" sticker and sell it. It might or might not go on Craigslist. (if it is listed the ad finishes with "and many more cars like this so some in and see") If the dealer gets too many in on trade the rest go to an auto auction.

Remember, the dealer knows all the numbers that the leaser isn't told. The company who backed the lease 2-3 years ago did their best to make sure that when the car was turned in the dealer would look at the remaining value and think "profit if I buy that and sell it". The dealer is going to pay the lease company for the rest of the value of the car. If the dealer decides there isn't enough money in selling it the lease company has to send the car to an auto auction and see what price they can get. (I suspect that a lot more goes on in these cases but I don't know what)

Me, because it came with a 7 year warranty. The price was good and the dealer offers a shuttle to and from my work (or my home) when it is in for maintenance.

Someone who needs a loan? I've bought/sold several cars on Craigslist, and it's always all-cash. Perhaps it's possible to get a loan from a bank to buy a car off CL, but it's easier to do so at a dealership.