Most ICOs that are not successful are considered by many as scams. I think this is a bit unfair. It is not good to consider this as a criteria for judging a an ICO as scam. I think the best way to look at the ICO to be a scam is by checking the team behind it, if they are actually the person as named or just somebody who pretended to be. Second  is that products are developed and without any visible product to show these means they are certainly a scam and the last one that I would be considering is that if the ICO is asking for payments and offers impossible or too good to be true bargains just to attract customers.