My streategy eventually became refusing to deal with it, and prodding them to develop a relationship with a local computer store - if I can't answer something in a single sentence or two, I say it's too complex to explain and they should have someone look at it. This didn't go down that well at first, until I got them to agree that they wouldn't try to fix their car this way if I was a mechanic, and trying to fix their computer without being able to see it was just as inefficient.