All the research in the world done by the mamas and the papas (no jokes, please), cannot substitute for getting to know a person’s actual personality with YOU. Just as a small example, unless he has been out to eat at a restaurant with the boy, a Rosh Yeshivah or rebbie has no idea how a boy treats the wait staff, if he is a conservative or generous tipper, courteous when asking the girl what she would like to order, etc. And since many yeshivish couples do not often go to a restaurant until the boy feels it’s worth spending that type of money (at least one or two dates, from what I hear), these are things even the girl will not witness unless she keeps going out with the boy.
There are many middos or lack thereof, that only first become evident over time, when the natural tendency is to relax ones’ guard. I went out with a fellow with whom I was fixed up after a couple of years of hearing about how wonderful he was, how smart, how learned, what good yichus, blah, blah, blah. I was very excited about meeting him. it was not until I actually DID meet him that I saw that he was a bit slovenly, very uncaring and blase about the date altogether, and he did something that showed he was not quite so terrific as his portrayers thought him to be. All the research in the world would not have shown me that until I saw it firsthand.