It’s theoretically possible to hand select and destroy files that might hold personal data, but the way thing are scatters around you need an expert [which I am not] to locate everything.
You could start with CCleaner, set it for Options> Settings> Secure Deletion, 7 passes, select every checkbox in the cleaner and wipe all the normal user tracks. Do the same with the registry cleaner.
Revo Uninstaller has a number of tools designed to cover one’s tracks, including one to shred previously deleted files. It also has an “Unrecoverable Delete” function. Use it to shred your entire user folder, if possible. [Would you have to log in as another Admin to do that?]
Make sure you have Windows Explorer set to show hidden files and folder as you look around for files to shred. Shred the hibernation files, C:\hiberfil.sys, and the page files, C:\pagefile.sys. They contain records of past activity.
There may be lots more you would have to do. I don’t know. Like I say, I’m no expert. It all depends how likely the buyer is to examine the drive and how damaging any personal information would be if discovered.
