Yosef Karo

“ And a prayer leader that who has aged and wants to appoint his son to assist him sometimes, even though his son's voice isn't pleasant like his voice - if he fulfills the rest of the things, then his son take precedence over anyone else and the congregation cannot prohibit him. ”

“ Someone who is not bearded: anyone for whom it is recognized that he has arrived at the general age where it is proper to have filled in his beard, we call him one who has filled his beard. If he is 20 years old, even though he doesn't have a beard we appoint him. ”

“ One who is free of sin; who has never had a poor reputation, even in his youth; who is humble; who is acceptable to the nation; who is skilled at [liturgical] chanting; whose voice is pleasant; who is accustomed to reading Torah, Prophets, and Writings (i.e. biblical text) . ”

“ A permanent leader goes before the ark himself and doesn't wait until someone asks him to.
16 מי שאינו ש"צ קבוע צריך לסרב מעט קודם שירד לפני התיבה ולא יותר מדאי אלא פעם ראשונ' מסרב וכשיאמרו לו פעם שנייה מכין עצמו כמי שרוצה לעמוד ובפעם שלישית יעמוד ואם האומר לו שירד הוא אדם גדול אינו מסרב לו כלל:
One who is not a permanent leader must decline a bit before he goes before the ark, but not too much ”

“ We don't appoint a prayer leader on the basis of the singing even if most of the congregation wants him.
22 שליח צבור בשכר עדיף טפי מבנדבה: הגה ואין לאדם להתפלל בלא רצון הקהל וכל מי שמתפלל בחזקה ודרך אלמות אין עונין אמן אחר ברכותיו [בנימין זאב סי' קס"ג ואגוד' פ' כיצד מברכין] :
A paid prayer-leader is better than a free one. ”