My response to MR Shopkeeper, would have been something along the lines of, "Oh my God! you mean there is an electrical fault with these PC's? I'll have to inform Trading Standards! I could have been electrocuted. Any chance of my money back?"
If something like a switch, which is obviously going to be touched by the user, can short out then the manufacturer could be prosecuted.
What happened "next". Did your friend accept the explanation?