I exclusively buy used cars directly from other people. I've only paid cash for every car I've ever personally owned; I don't believe in haggling with dealerships. My first car was $1K, my second car was $3K, my third was $2.5K, my fourth was $4K, and my fifth was $6K.

Then my sixth and current car was actually $17K, but it was a brand-new 2017 Mazda 3 Grand Touring edition with only 7K miles on it. A buddy bought it as his college commuter, then didn't start up classes for a few years. It sat in his garage, mostly untouched for 3 years. Then COVID hit and he decided to sell it for extra cash, so I got it for super cheap.

The key is to take the used car to a repair shop before you buy it (preferably while you're doing the test drive) and pay for a quick diagnostic. If everything looks good, then buy. You won't have to worry about buying a junker. Some people have really good condition cars and underprice them while trying to sell them (usually folks who need to get rid of it quick, or make some quick cash).

My wife insisted on buying a car from a dealership, since she'd only owned hand-me-down POS junkers all her life. I posted about it in another comment here, but she got an H6 Subaru Outback for 10% under the MSRP price, a deal because we were active duty military at the time. So we paid $34K for it. Besides that, it's personal sales, cash up front, no debt to pay off or anything.