HipHopScribe
Headphoneus Supremus
Should I assume they came in contact with crap, piss and toilet water?
Realistically if you leave your house you're coming into contact with someone else's crap, piss and toilet water on shared surfaces on a daily basis. Buying someone's used headphones is much lower risk than going anywhere and touching a door handle. If you're really concerned buy new headphones rather than used, not that you have any guarantee someone working in a factory somewhere didn't touch some part of your headphones or the box with dirty hands.
Also, I would probably avoid anything like alcohol or clorox wipes as those are likely to degrade earpads material. It's probably fine to do it sparingly, but otherwise a mild soap and a little water is safer, slightly damp and then quickly dried for most earpads.