Why do we sell chametz through a rabbi?

Kolel L'horaah Ma'asis Crown Heights - Shiur 19 on halachic topics - by Rabbi Shraga Dovid Homnick, Sgan Rosh Kolel, on the origins of the practice of selling chametz on a communal basis through a rabbi, and the arguments of those who thought that far from an improvement, this made the sale illegitimate

https://www.youtube.com/watch?v=FpYYgOdnUlw