You guys (oops and girl, Amber) hit the nail on the head.

I agree there is usually no need to be aggressive with the person who is looking sketchy ... just offering to help, asking some questions, and telling them a few horror stories is enough to get their attention.

Done this a MANY times.. the last time I did it at lassing the rider quickly made his own wise decision not to launch a 16 in 25. I offered to meet up with him later when the wind came down and keep an eye on him (for help not judgement).