Our Mishna on Amud Beis addresses the topic of the Jewish slave, discussing the requirement for a Jewish slave who chooses to extend his servitude beyond the prescribed six years to undergo a ritual that involves piercing his ear.

The Gemara later on (22b) elaborates on the significance of this ritual:

Rabban Yoḥanan ben Zakkai would expound this verse as a type of decorative wreath [ḥomer], i.e., as an allegory: Why is the ear different from all the other limbs in the body, as the ear alone is pierced? The Holy One, Blessed be He, said: This ear heard My voice on Mount Sinai when I said: “For to Me the children of Israel are slaves” (Leviticus 25:55), which indicates: And they should not be slaves to slaves. And yet this man went and willingly acquired a master for himself. Therefore, let this ear be pierced.

Certain understandings of this concept indicate that even selling oneself for six years is frowned upon, although it is not categorically forbidden due to extreme poverty. But when he repeats the act of selling oneself, while not appropriate initially, compounds the issue and makes it more problematic. For an extensive discussion on this perspective, refer to the following sources: Maskil Ledovid commentary on Rashi Shemos 21:6, Chizkuni ibid, Bartenura on the Torah ibid, and Riva ibid.

Yismach Moshe (Mishpatim 6:2) raises a question: How was it permissible for Yakov to "sell" himself into servitude to Lavan (Bereishis 29:18)? He answers that when Yakov initially agreed to work for Lavan, he stipulated that he would work the seven years before marrying Rochel. This condition allowed him to remain unencumbered since he was free to change his mind during that period. However, a challenge arises with the second set of seven years he worked after Lavan deceitfully substituted Leah for Rochel. In this instance, Yakov married Leah immediately after the Sheva Berachos (Bereishis 29:27) and subsequently obligated himself to another seven years of labor. Yismach Moshe contends that because Lavan initiated the agreement, Yakov wasn't genuinely obligated. Rather, he chose to honor his commitment out of a sense of integrity.

An inquiry arises from this explanation. The Gemara in Bava Basra (47b) teaches that even a sale made under duress is valid since the recipient ultimately accepts the payment. This principle seems to contradict the assertion that Yakov wasn't bound by his agreement with Lavan due to the latter's coercion. 

However, we may answer this with another precedent set by an earlier Gemara (13b), which permits engaging in subterfuge to recover what rightfully belongs to an individual:

The Gemara further relates: There was a certain woman who was selling belts. A certain man came and snatched a belt [varshekha] from her. She said to him: Give it to me. He said to her: If I give it to you will you be betrothed to me? She took it and was silent, and Rav Naḥman said: She could say: Yes, I took it, but I took my property. There is no proof that she agreed to accept it as a betrothal.

Applying this principle, one could argue that Yakov's second agreement to marry Rochelwas actually a method to retrieve what was rightfully his. In fact, his commitment to work an additional seven years was to reclaim what he was entitled to from the outset. Nonetheless, as the Yismach Moshe concludes, Yakov upheld his word out of honor and integrity.