Whether you are looking for a room or for a roommate, it usually starts with an ad in the classified section of Craigslist, a profile for those using Roommates.com, or threads that you start or follow on Reddit…
And then many exchanges of messages over several days, frequently writing the same thing. Forgetting who wrote what… or forgetting to answer…
Hopefully, at the end, a meeting IRL.
What about reversing the process? Meeting first - virtually - to get acquainted and check compatibility on both sides. As it is virtual, several potential roommates can discuss simultaneously with the room provider…
And then, if there is no fit… you just move instantly to the next virtual room… In one hour you can probably explore 10 opportunities while staying home.
Virtual is not the same as actually meeting the person, and that may not necessarily determine anything unfortunately until you actually live under the same roof for a spell. Anyone can say anything online but how do you know that is the truth or representative of the person?
Personal referral from your inner circle of friends or family is probably best. Your inner circle should kind of know how you are and would have an idea if there is a match or not.