feh sometimes you don't even need that much, people talk, and you can guess on what you heard, most of time I overheard people talking about others, and I just heard like a phrase or 2, normally that is enough for me to guess what they are talking about, and after some months I heard the whole history and yeah I guessed right.
but the real question here is you not needing to do it, if you do is just to have info on things so you can use to your advantage later, i'm all up to know more then you lot others know and save it till you really need to use it, but in a dating context you shouldn't care, if your gut feeling tells you foul play you start to look around, if you in a marriage and need some info for the divorce, check what is legal and can be used or just to know how to prove it later its ok