Honestly it is hard to identify the scam projects because all we know that scammers are not an idiot. But for me scam project are having a very good offer but while the project is on going suddenly all of features and procedure while change. And a good project will be recognized by it's existence and number of participant that will have and continues growth.
That is very common, many people think this only happen in bounty campaigns when the developers change the rules but this happens all the time, I see many projects with a road map but as soon as they begin the development of their project they begin to change the dates of when things will be ready and people just accept the delays but most of the time there are no delays because they are not really working on the project and they are just trying to find the best moment to disappear.