In reply to johncook:
John, sorry to hear about your experiences, and glad you are alive!
It took me a long time to realise that when I asked people new to me how good their belaying was, they would always answer, "fine", or "good", never, even if they had only been indoors and NEVER held a fall, "not sure", or "ok, I think, but I've only held one small fall". What was happening was a disconnect between what they meant by belaying (paying out the rope), and what I meant (holding onto the string if I pull a block off). Being that the rope will pay out very nicely if you just stack in on the ground carefully, they we not belaying at all, but to be fair to them, they did not know it.
I now approach things in a way that might overcome this confusion and simply ask if they have held many large, unexpected, falls outdoors. Or what the biggest fall they have held is. This seems to both extract the correct information, but also resets the level of expectation about the adventure they are about to commit themselves to as we stand on the edge, about to abseil into the Boulder Ruckle.
I guess the rule is, don't get on the plane if the pilot has never landed a plane.