Nice question if the exchange has reputable people and known by the community, I think that's one good factor to know that they are sure with what they are doing. I know you are worried with those exchanges that are just coming like mushroom.
They will pop and soon they will be gone. You will later notice that the new exchanges are sure with their operation if there are many users and volume is good on them.
Yes, but how do you know which is a mushroom. (Well, maybe not know, but suspect)
Suspect is your personal instinct but it's not enough indicator to know if that exchange is just like the mushroom definition that we're using. Observation will do, like for few days, week or even up to a month and see on how the exchange's behavior.
With that time span, you can determine already if that is true or just displays decoy as their front.