I think there are various factors that you must check before investing in an ico that proves whether an ico is legit or not. The most important factor that you must always look for are the ICOs with a working product as these ICOs have higher chances to be legit.
The other thing that you must consider is the idea of the project. Always look for project with unique idea as these icos have higher chances to grow in future.
What kind of product you mean bro? I see most of the project comes to market are only on the online platform and some smart contracts and etc. If you are worry to know how to find the best project. You should read the white paper shared by them. Then you will comes to know whether it is legit project or just a scam.
One more idea, You can check their linked-in and other social media site accounts. You can understand it better.