Our Gemara on Amud Aleph uses a scriptural derivation and comparison between real estate and Canaanite slaves. Just as the regular laws of overcharging or undercharging do not apply to real estate, so too, in regard to slaves, they do not apply.
Rav Yonasan Eibshutz (Yaaros Devash 1:17) uses this ruling to explain a deeper idea behind Esther’s plea to Achashverosh (Esther 7:4):
Had we only been sold as slaves, I would have kept silent; for the enemy is not worthy of the king’s trouble.”
Esther was arguing though Haman had paid 10,000 silver to the king for the rights to exterminate the Jews (3:9), it was an unfair exchange. Esther said, granted if we were sold as slaves, there is no overcharging or undercharging. However, the Jewish people are not to be considered slaves, and no sum of money is equal to their worth.
I have remarked numerous times on this particular genre of rabbinic literature that inserts lomdishe arguments into the motivations of Biblical characters. It is important to consider that although it sometimes may seems absurd when the Midrash attributes Talmudic reasoning even to the likes of Pharaoh (see Sotah 11a), it is not to be taken literally in the sense that Esther presented a “Chaburah” to Achashverosh. Even if Esther possessed such Torah knowledge, why would Achashverosh follow her litigious analyses? Did he attend Yeshiva? The rabbis are in touch with a deeper idea. Torah morals and concepts are intrinsically and intuitively valid, therefore the various motives and reasoning are captured metaphorically in anachronistic lomdishe projections, but they represent the compelling underlying morality. Esther is arguing to Achashverosh that the Jewish people are not a commodity and should have not been up for sale. Even though literally her words state that she would not even bother the king if her brethren were sold as slaves, she is still hinting at the opposite. She is subtly rebuking Achashverosh for commodifying the Jews. Since she is talking to a king, as is in any dissenter in a tyrannical regime, one must be subtle. It’s a clever and underhanded way to argue in front of Achashverosh, or even to protest in such a way that it is deniable.
I believe the Midrash often uses metaphor to capture an unvoiced double entendre, even possibly unconscious. Such as, Yehuda says to the ruler of Egypt, “You are considered as a Pharaoh.” (Bereishis 44:18) Ostensibly this is to flatter him that he is almost as great as Pharaoh, but the Midrash says (Midrash Rabbah 93:6 and Rashi ibid) that Yehudah was implying, “Just as I’m not scared to fight Pharaoh, so too I’m not scared to take you on.” Could Yehuda have really said that? Why would that be wise? This would just instigate the ruler instead of appealing to his mercy, which the rest of his message conveys. The answer is that there were subtle rebukes and maybe even unconscious expressions of Yehuda’s inner feeling.
The idea behind these Midrashim is that human communication is often laden with unexpressed and sometimes even unconscious messsges, which can be the opposite of what they are saying. An emotionally intelligent person learns to listen and notice what is expressed between the lines.