Don't be afraid of Craigslist. Even if you don't feel knowledgable, you can make a list of things to watch out for:

-Wheels spin straight without wobbling
-Tires have tread, and sidewalls not disintegrating
-Parallel spokes are firm and only give a little bit when squeezed (when I was looking for a CL bike I found a few vintage rust-buckets where I could squeeze spokes until they touched)
-No major rust issues (a tiny spot or two where paint has chipped may be okay).
- No dents or bends in the frame or fork
-Brakes responsive and smooth. Brake pads shouldn't touch the rims at any point when you are not braking. Also, check that the brake pads are not disintegrating at the surface where they touch the rim to brake.
- Gears (if any) shift smoothly
-For a single speed: chain-line looks straight (and chain doesn't skip or fall off during a long test ride). Chain should also not be sagging at all.
- No clicking, scraping, or other bad noises from the bottom bracket (where the crank arms rotate)
-AND importantly: you feel comfortable, and confident after a long test ride.

And another thing with CL: often you get a good or bad feeling about a seller so trust your gut.