How can I identify and uninstall all apps installed by a certain user? I have a Macbook that was also used by a previous employee of my job. I made the mistake of not reformatting the entire thing when I installed it. Now I have a new Mac app store ID, but the apps previously installed under his ID keep asking for his app store password - my assumption is this is to update themselves. 

How can I identify and uninstall any apps previously installed under a different Mac App store ID other than my current one?
I think your best bet might be to come at it from the other end of the problem.

Open App Store, sign is as you if you didn't already, then check your own Purchased list.
Anything not in that list will belong to someone else.

Unfortunately, that will likely include the OS itself, which may cause future issues, especially if you don't know the old user's credentials, or if they ever change the password.

Wipe &amp; start afresh would have been better, in the long run.