Got one of those calls a couple months ago while at home waiting for my wife to get back from shopping. Had time to kill so I played along. I became the most inept computer user ever as this poor scammer tried and tried to walk me through some Windows admin tools and event logs which would "prove" that my computer was horribly infected and ready to explode. I'd ask every time "do I left click or right click?" even if he had just told me. I'd use wrong terms to describe thing, I'd say "oops, what happened?" under my breath and say "What was that last part again?"
All that was leading up to getting me to download their "repair tool" which was certainly going to be a virus. After 20 minutes of my incompetence and bumbling we were at the point where he could direct me to the website.
I unplugged the network cable from the PC. I feigned ignorance about Internet Explorer, he told me how to start it, I read off the (actual) error about not being connected to the internet. He asked me to try my email, I said I didn't use email.
He asked how I used the internet, I said I don't know. Do I have a router? A modem? I said I don't know. I could hear it in his voice - all that time wasted on someone who COULD have been scammed, was WILLING to be scammed, but didn't have an internet connection to make it happen.
Felt kind of good, maybe I saved a couple other people from being harassed.