Like the other guy stated, we can't since we didn't know what will be the final phase of the project. But there are factors we can check to minimize our worries and the associated risk which some are; having an  active devs, funds being escrowed and continous development.

Investing in ICO is really a risky investment but if we will take the brighter side of the picture it will be profitable. So it's really worth to try than to try other risky investment out there.

You can have an assurance that an ICO will be legit enough. It is like or even more than gambling just like what bathrobehero said. Just look at their road map if they are planning to make their coin for a long term use then go for it. Read their ANN thread and together read the people's comment , that is important.

You can always wait until it hit a major exchange.

The first thing to do is are the faces of the developers visible and what is their antecedent in crypto space
Second, how visible is the technology or idea they are proposing
Third, A trusted Escrow must be used
Fourth, invest only after the project get traction.

All these are not guarantee but will help to help your decision making

It is not possible to predict that Ico is successful until the final phase of the project, every thing looks like genuine but when they din't reach their definitely it will be bad ICO. Don't consider ICO without any escrow, escrow should be their so that escrow will hold you money until they need to finish those which are listed in RoadMaps.

Invest on ICO is such as placing a bet for some card on the board. You don't know which card is good but gamble on it is really interesting.
You can't predict which ICO will success on the progress, but support they coin will make a +1 for development.

I'll definitely look for existing project not empty promise where they can run when the dev received the funds,some of the legit ico I invested are BASH and Victoriouscoin,victoriouscoin is implementing an Ics and they have ready projects while holding their interactive coin sales.

change one letter and like magic you have a whole world of legit options. here they are - http://www.nasdaq.com/markets/ipos/

Can't remember I've read more stupid comment than this recently.