I’m going to have to agree here with what another poster said. Paranoid and shrewd are incompatible traits in this context. If you’re shrewd, you think you can weed out any scammers. That’s the opposite of paranoid, who’s certain they’re getting screwed by everyone.
I live by my computer too, just finished my first book - they’re finishing proofs at the publisher now, and starting a new one. I can’t afford to be down either, I have deadlines to meet. I just don’t have 4k lying around without having to overstretch financially.
In your case, it sounds to me like the only way you’ll be able to sleep at night is to buy a new one on sale from a reputable retailer, or refurbed from Apple. That’s a perfectly reasonable position to take. Don’t get caught up in trying to save a couple hundred bucks, if it will stress you out.
One last thing, I don’t know how many MacBook pros you’ve had, but I’ve used AppleCare for every one I’ve bought new, the 2015 I have now is the first one I haven’t bought either refurbed from Apple, or from a campus store. I’ve had to get displays repaired, new logic boards, entire machines replaced.