I've bought multiple Macs on eBay and Craigslist with no problems. Most will sell with a fresh install of MacOS and if in person you can check everything out. If buying on Craigslist I like to do the transaction somewhere with a good internet connection. That way I can check that it's operating properly.
Which 2019 models? You do not want one with the butterfly keyboard.
FWIW, quite a few Apple Certified Refurbished 2019 MacBook Pros are available. They include a full one-year Apple warranty, the same as a new Mac, and are also eligible for AppleCare.
You DO NOT want to buy a 2019 MacBook Pro if...
- it's a 13" with the butterfly keyboard
- it's a 15" with the butterfly keyboard.
The butterfly keyboard is highly-prone to failure.
And when it fails -- EVEN IF IT'S ONLY ONE KEY -- the ENTIRE top case of the computer has to be replaced.
That's going to cost you $750 or more -- JUST FOR ONE KEY.
Apple currently has an extended warranty on the keyboard, but it's for 4 years from the date of purchase. That means the warranty on a 2019 MBP will run out next year.
Do you really want to take a chance on one of these?
Having said that...
The 2019 MacBook Pro 16" has the improved "scissors style" keyboard.
Completely different design. That might be a worthwhile buy.
But having said that...
The best place to buy a "used" MBP is from the Apple Refurbished online store.
Then you KNOW what you're getting.
I would agree with the opinion above, please do not buy the butterfly keyboard model; and I would also avoid the Intel 2019 models too. You’re better of spending a little bit more and going with an M1