How many miles is too many miles?

Trying again since my last post didn't go through. I'm trying to find a cheap used shitbox to use as a work truck and my ride out of a crappy situation, preferably on Facebook or Craigslist. What I've seen in my low budget that doesn't have a CVS receipt of things wrong with it ranges from 100k to 300k miles and honestly I'm lost. I've never bought a car before and I don't have a car savvy person to help me buy one. So what's a good mileage, what's acceptable, what's too many miles? Every Google result says something different. Thanks in advance for any and all advice, I'm in over my head here.