How often were you scammed in the past considered in percent of all campaigns? How many were paid? And do you have an idea to avoid it?
Getting the answers in the right percentage as you seek it will be a difficult task, except you have a core mathematician here who can spare that time. I think it is a thing of regret to do a task and not get paid for it. I have experienced that two times here. But what happened was that the developers scammed investors at the end of the ICO and ran away. This now makes me want to stay away from bounties paying in coins not trusted and listed.