I didn't watch the videos all the way through, but from what I gathered, the snakes in those youtube videos either came into direct (or nearly direct) contact with the heating pad, or the cause wasn't specified. I am wondering if the pet store employees meant that the plastic of the cage you were talking about would be enough of a buffer to keep the snake from getting burned even if it rested on the bare plastic? (Or were they counting on substrate to protect the snake?)