In my opinion, you can determine it just by looking at their activity on social media.
When they start acting weird, then it would be the last time you will see them
yeah, that's one of the reasons we suspect they are a project scam. they will start giving many reasons to avoid any questions from investors and of course as you said, that will be the last time we see it.
even more painful, they will look strange when they have managed to get a lot of funds from investors and make bounty hunters work hard to promote their scam project for free.