You are experienced with computers.... if a massive amount of pop-ups of illegal stuff loads and spams on boot that's probably a virus and not some sicko. Wtf regular computer does that? Fuck investigating that would ruin my psychology, I would turn it off say you have a virus or something I'm not willing to delve into. Go to the FBI of you want to salvage data.
Massive pop-ups? That's the only way viruses behave? I was unaware.
I've cleaned hundreds of PCs with massive infestations of viruses. 80% could be cleaned in a few days with no trace left. Other's needed to be reloaded because there could be no risk of it remaining. That meant reinstalling every PC workstation and server on the network.
Most viruses don't do pop-ups. They wait silently, and the only way you know they are there is if you do a scan -- manually or automatically.
Stop pretending to lecture me. My years of experience stack up well against any hypotheticals you can conjure up.
What you would CHOOSE to do is not any kind of "standard." Individuals choose for themselves how far they will go into a disk. Perhaps the drive has important data for which there is no back up? The customer may want it recovered.
If you offer PC services and are unwilling to do work on a virus-infected PC with NO CLUE about the nature of the virus, then you are not a repair shop owner. You're just a guy who knows about computers and is willing to do routine remedies for people who don't understand PCs.