Sforno on Exodus 21:8/ספורנו על שמות כ״א:ח׳

1אם רעה בעיני אדוניה, even though the normal procedure is what we outlined in verse seven, her “master” does not have to marry her if he finds her incompatible, as otherwise he would eventually come to hate her. However, in such a situation the father and the master have to cooperate in releasing her from her obligation as servant.

2לעם נכרי לא ימשול למכרה בבגדו בה, the father of the girl in question who had already betrayed her by “selling” her initially. We know that even Lavan’s daughters were angry at what they considered their father having done when he “sold” them into marriage. (compare Genesis 31,15) The Torah describes here the negative impression it makes on any of his peers when he observes a Jewish father selling his daughter’s services for something other than marriage. Once an employer/prospective husband, has done this no other Jewish father is allowed to sell his daughter to such a man. [the word נכרי does not refer to a non Jew, but to a Jew who acted contrary to Jewish mores. Ed.]