Maybe if they are having problems, offer a clearly sub-optimal way to do it, and try to get them to talk about why it's not great or what better ways might be.

Maybe if they are having problems, offer a clearly sub-optimal way to do it, and try to get them to talk about why it's not great or what better ways might be. That might help uncover some thought pattern or understanding about it. Such options could be FTP, as an email attachment, or the body in a single HTTP POST. They should be able to come up with thoughts about security, speed, reliability, etc.