There are basic steps to identify the legitimacy of a start up project but they are not 100% guaranteed effective as you already experienced. Learning from the lessons of 2017, a verifiable team is one of the best deterrent and it's at the top of my list. You never really know what they have in mind but they would think twice before scamming if people know their real names/faces. Having an aggressive marketing campaign is a 50-50 for me. It's either they are serious in securing funds to develop the project or they are desperate to take your money.