A bad roommate can ruin the good interiors or the convenience of having complete amenities in the apartment. So, before you even commit to renting an apartment where you will have a roommate, you should check out the roommate first as well.
When you drop by to inspect the apartment, take time to talk with the potential roommate. If the roommate starts foul mouthing other people, you should be cautious as he or she may be hard to live with. Imagine if he foul mouths you in front of other people.
The roommate may have the tendency to meddle too. You should try to detect this during your first meeting. Otherwise you would find a roommate who would not only be too meddlesome. You would even no longer have your privacy with someone like that. Your life would even be broadcasted. 
Another thing that could be bothersome between roommates is hygiene. Some would have dirty clothes all over the apartment. Some would not flush the bathroom bowl after using it. Toilet paper would be scattered. What's more is the roommate could have bad personal hygiene too. Surely you would not want a roommate who has bad body odor. And so again, do not just inspect and observe the apartment. Get to know the roommate as well.