Lot of the members already pointed out various reasons
Would like to add
a) If it sounds too good to be true, then definitely it is not true ; Else they would not have come through the ICO mode to look for funds
b) Team , Team and Team: Will will be difficult to find out that ones that are likely to scam then find out the ones that are unlikely to scam ( so can be used only as a filtering criteria) .
c) Working product: If it has a working product or a beta version then unlikely they will scam as the benefits of the project would be more than they will gain from scamming