Sforno on Genesis 12:13/ספורנו על בראשית י״ב:י״ג

1למען ייטב לי, so that when you will say that you are my sister, each one will entertain the hope that I will agree to your marrying them. Therefore, none of them will have any reason to kill me. Rather, he will seek my approval by offering me a dowry for you. It was the custom in those days that the father of the bride would be bribed with money or its equivalent to agree to let his daughter marry someone. This also explains why the Torah speaks of מהר ימהרנה in Exodus 22,15-16, i.e. “he (the seducer) shall pay a heavy dowry,” and why the option to refuse such a marriage is not so much the girl’s but her father’s, as we see from the verse following.