Thank you so much for the info.

I'll be able to tell if the taper is messed up by looking at it? I've seen extreme examples that are obvious.. but what about something like this..
Here's photos of a used pair that are constantly being sold in Japan




Could these tapers be worn and messed up? Or is it real easy to spot by looking at them?
If the naked eye can't really see it spot-on and my cranks look like that (theoretically, lets say those crank arms are toast) this would explain why the mechanic didn't say anything today. I told him the crank bolts had been coming loose so he recommended some Sugino 8mm hex crank bolts.

And you go judge by the inside of the crank arm, not the outside?