On loops and rolls, I do like to get them doing a loop pretty quickly, if they master keeping it straight and level. For most folks, that's not a problem. I figure getting used to looping might help them recover from a mistake.

On test flights, I agree there is a difference between a beginner and someone who is just slapping things together with out paying attention to details.

Duct tape as a structural component huh? I dunno about duct tape, but I do burn though a lot of packing tape . It's amazing what you can get to fly with enough tape and a big enough engine. Ok, I'm kidding around here, but I do know what you are talking about. I have said to someone "gee, if it was my plane, I wouldn't fly it, and here's why, but if you insist, and you recongnize that it might come apart in the air, I'll fly it for you."