Mac King Fu:

Knowing how much a Mac has actually been used by its owner can be very useful if you’re buying pre-owned. A Mac three years old that’s been used very infrequently could be a better purchase than a two-year old Mac that’s been left running 24/7, for example.

While physical condition of the Mac gives a clue, you can garner some further clues by a little software probing. It’s not entirely accurate, and comes with substantial caveats, but could be worth a try.

Very interesting read. I definitely learned a few things about the myriad of data in the System Profile app. Useful if you are buying, also useful if you are selling.

Note that option-clicking on Apple > System Information… is a shortcut, bypassing the more traditional Apple > About This Mac menu item.