Great points, promising unrealistic returns is definitely a red flag, it's unethical and often illegal. Here is my criteria for selecting an ICO https://steemit.com/money/@crypticat/ninelives-of-icos
One red flag is how they vet investors. Do they do KYC and require proof of ID? Some coins allow people who are from countries which have banned ICOs to participate. This disregard for the law is a huge redflag.