In addition to what has been mentioned, if you want to check if an exchange is legit, just try to look it up on CMC. If there's nothing about it, you should stay away from it. This doesn't mean that you should use any exchange on coinmarketcap though. It's just that the criteria to be listed there are not that simple, not for someone who wants to scam people and earn a quick buck anyway.
Although there are many exchanges, I still choose the top exchange. Of course, I also reserve my opinion. I don't like centralized exchanges. There are too many deceptions, too many routines, and too many temptations. In short, decentralized exchanges are my current choice.