Can you be specific the first thing that indicate to you an ICO might be a scam ?
When the ICO is published these developers will have the road map and with white paper published on their respective media. These documents clearly states that how much the team is going to hold and for how long. If they are going to hold it only until the listing to exchanger then there is possibility that they will see out huge amount of coins leading to dumped prices.
For this to overcome, genuine ICO team will publish clearly that any unsold coin during the ICO crowd sale will be burnt away meaning those coins will never exist there for buy or sell by anyone. Thus this makes the sense of reality where you can have assurance of devs team not gonna mess with the coin before you.