To truly know if someone is a computer nerd or just a poser you need only look at their input technique.
An occasional user will primarily use the mouse, only touching the keyboard to enter in text or web addresses. You can tell they are occasional because they type in their url and then use the mouse to click “go” instead of hitting the enter key.
Someone who uses the pc mainly at work will know the basics such as “Ctrl+C” and “Ctrl+V” but are unaware of the magical Windows buttons such as “Windows+M” or “Alt+Tab” or Mac keys like F11. Mostly they will just right click to copy and paste.
Someone who is a gamer will have one hand on the mouse and the other hand on the keyboard at all times. One hand is “Ctrl+C”ing while the other hand is selecting text with the mouse. If you’ve ever seen someone play Doom 3 you’ll know what I mean.
Finally, the 24hr puter person ignores the mouse altogether, opting for complete keyboard control. They’ve probably ditched the gui altogether – preferring the terminal or command line. If still in gui mode, they have memorised every shortcut key possible and tab all over the place. They have a scroll mouse but prefer to use the page up and page down keys, and to go backwards in the browser they use backspace. The mouse will be pristene clean.
So, if someone offers to fix your computer, watch them closely as they navigate around the screen. If they sit down and immediately head for the keyboard you’re safe. If not, make sure you have a recent backup!