Actually there is a big difference.
You should trust project when you join ICO. Because only important thing is just projects worth. And there is no one you can ask what is going on except project team.
You can trust the exchange which runs IEO. If exchange is good one, it is hard to list trustless project. For example, we can always trust Binance's IEO than many other ones.
So there is a middleman in IEO. And if it is trustworthy, project is also.
And I know that many exchange listed scam IEO's. So we won't trade in that exchanges anymore.