I'm trying to fix a laptop give to me by a user who reported to me that when logging out they don't wait for the laptop to logout completely, and instead immediately shove it in their bag (without even turning the laptop off). This makes me suspect that all of the corrupt files the computer keeps reporting are due to this behavior, but I can't really prove it, so I was wondering if anyone knew how to tell if a computer or hard drive has been damaged by overheating while in someone's bag.
It is unlikely to be overheating. Any reasonable laptop will have a thermal shutoff and, in any case, electronics really are not that sensitive to heat. Certainly running constantly hot does reduce lifetimes but other than that, the main impact is in rapid changes in heat not just running hot.
Far more likely is that the hard drive has been operational whilst being jogged around. The heads on a drive are less than a hair's width from the surface and drives are very susceptible to movement damage.
Putting in a replacement drive (e.g. from another laptop) would show if it is a general laptop issue or a drive issue. For drive issues, you might well be able to fully recover if the damage is not too great by using Spinrite.
For future reference, put the laptop to sleep before moving and next time, buy one with an anti-drop feature such as some of the Lenovo's and HP's.