Sex cams send a request to them and get private
Did some gorgeous model just send you a friend request?
If their Facebook timeline says they joined Facebook 12 days ago then the person is most likely trying to scam you, unless it's your grandmother, who is very late to the Facebook party and has a legitimate reason for having a limited history.
Depending on who the person behind the fake profile is targeting, you will likely see friends that are predominantly of the opposite sex of the requester since that is likely who they are targeting when they send out their fake friend requests.
If the request is from a lady targeting men, expect almost all men in the friend's list, instead of a mix of men and women like you would expect from a real person.
If you can't recall ever meeting this person in real life or meeting through any mutual friends, then it is likely a friend request sent to you under false pretenses.
Check their friend's list (if it's viewable) and click the "mutual" list to see whom you both know.