The Shulchan Aruch, Even Haezer 49:3 rules that:
כל מי שאינו בקי בטיב גיטין וקידושין לא יהא לו עסק עמהם להורות בהם שבקל יכול לטעות ויתיר את הערוה וגורם להרבות ממזרים בישראל:
Anyone who is not an expert in the nature of divorces and marriages should not deal with them to teach (about them, because it is easy to err and to permit an erva [that is, a forbidden woman] and cause an increase in mamzerim [that is, children born from illicit relationships] in Israel.
Namely, in regards to halachik ruling purposes (ie not a mesader kiddushin) only experts should deal with matters of divorce and kiddushin.
Since (to my knowledge) there isn't a special semicha given for this-- how is it determined whom and when a person is sufficiently considered an expert to rule in this area?