On a related note, there is a freeware gem called
Installation Analyzer that can take a before and after snapshot of the system to list all file and registry changes that happened during an installation. It's quite useful in determining what changed during an install and might give you a list of things to check to determine whether those 3rd part apps were actually installed.
However, to be 100% certain you are checking the right thing, it's probably best to go to the source as suggested by QOAL.