Never have invested to any projects during their pre-sale ICO/IEO. But the basis of how most of the investors relies on the project itself, what it offers and what it aims on why it has to be funded.
There are basis that relies on how reliable the people that are involved to that project and it's up on how you will study about their background carefully. Some were exposed from their past bad projects and how they got rekt being involved to that project that made their reputation bad.