there’s a good chance your malware is running as administrator as well.
If you really want to be a pro, you could save a clean configuration from a new install of Windows and put that on a flash drive to take with you. Save a new version every time you touch a PC for the first time to make sure you can quickly identify all of the new crapware the owner has added.
There's a great feature I didn't know about! Unfortunately, I'll probably only get around to doing this when I finally do a re-build where I actually stop to make a clean backup, too - i.e.: probably never.