What would you look for in a used bike when spending USD$150 / CAD$200?

Some background... this summer I'm spending 2-3 weeks with my folks back in my old hometown, and will likely be doing so every summer for the foreseeable future. They have a bike trail that connects to much of the city right in their backyard, so I'd really like to take advantage of that.

However, given that I'm talking about a relatively short amount of time, I really don't want to spend much on a bike that will sit unused for ~50 weeks of the year. I was checking out Craigslist, and was surprised by the number of bikes I saw available for USD$150 or less.

Obviously when buying a used bike at this price, you're making some significant compromises. But I'd like ask, if you all were buying a bike in that price range, what parts / aspects of the bike would you look at in particular? What might be something that would be a big red flag?

I'm capable of doing some basic maintenance and repair if I have a guide, but I'm not capable of doing major fixes.

(and apologies for the North American defaultism in the price range, essentially I'm asking for what you'd look for in an old, used bike that isn't a waste of money but not necessarily something you'd want to ride more than just occasionally, feel free to think of that in your own local currency).