I could not agree more with Hagar regarding installation of scenery and/or aircraft packages. I never "trust" auto-installers or instructions which tell you to unzip a file directly to some specified location.
Therefore I always unzip to a temp folder first, read through any documentation and then manually move items where they should go.
I have been bitten once too often by an improperly contructed self-installer or zip file.
I tend to trust well-known professional company's installers. I never trust "amatuer's" efforts however...
I use a slightly different technique though. I have two folders set up specifically for testing the actual installer and/or instructions:
C:\FS9_Dummy
C:\FSX_Dummy
This allows me to install or unzip to the relevant folder, and thereby see exactaly what gets put where...
Keep in mind that with commercial models, there are sometimes certain files that need to be placed in specific system locations (license files, .dll files, etc) that can only be done by running the installer program...