Travel Agent's Ethical Dilemma with Shabbat Booking

As a travel agent, I occasionally encounter situations where clients, who are non-observant Jews, request flight bookings that include travel over Shabbat. I am seeking your guidance on the halachic perspective regarding my role in facilitating these transactions. Is it permissible for me to arrange these flights? Additionally, from an ethical standpoint, what considerations should I take into account when processing such requests, knowing that these flights will occur on Shabbat?

Thank you for your question.
Your inquiry touches on a compelling subject: the ethical and halachic dilemmas involved in assisting or enabling a Jew who plans to transgress the mitzvot.
There are two Halachot to consider in this context:
1. Lifnei Iver Lo Titen Michshol - This phrase from the Torah, meaning "before the blind, do not place a stumbling block," serves as a metaphor to emphasize that Jews are not only obligated to observe the mitzvot themselves but also must not facilitate or enable another Jew to transgress. This principle underscores the responsibility to avoid leading others into sin.
So in your case of selling an airplane ticket to a non-religiose customer to enable him to fly on Shabbat, one might consider whether it constitutes a violation of the principle of "lifnei iver" (placing a stumbling block before the blind). However, the Talmud clarifies that "lifnei iver" only applies when you are the sole provider of the means to commit a transgression. If the individual has alternative means to acquire the same item or service, then the prohibition of "lifnei iver" does not apply.
This Chidush is derived from a discussion in the Talmud(Tractate Avoda Zora 6b):
"From where do we derive that a person should not extend a cup of wine to a Nazirite, or a limb from a living animal to descendants of Noah? It is stated: 'Before the blind, do not put a stumbling block' (Leviticus 19:14). But here, when they would not understand and take it themselves, he transgresses 'Before the blind, do not put a stumbling block'! The answer is - it applies where he stands on both sides of the river."
This Talmudic explanation shows that if the Nazirite is on the opposite side of the river and cannot access the wine without assistance, providing it would indeed be a stumbling block. Conversely, if he is on the same side and can access it himself, there is no transgression.
Applying this to the current discussion about booking a flight on Shabbat, if the buyer has other ways to obtain a ticket without your service, then it does not constitute a violation of "lifnei iver." The buyer's ability to access the ticket independently means that refusing to provide the service does not place a stumbling block before them.
Additionally, one could add that this situation may not be analogous to handing a Nazirite a cup of wine. The cup of wine itself is inherently forbidden for a Nazirite, constituting a direct violation of his vows. In contrast, providing a travel ticket does not inherently involve anything forbidden; the ticket merely facilitates travel. It becomes an issue only if the recipient chooses to use it in a way that violates Shabbat. Thus, the ticket itself is not a 'dvar issur' (a forbidden object) in its own right.
2. is the concept of "mesayea le-ovrei aveirah," which refers to the prohibition against assisting a fellow jew to sin. This principle underscores that one should avoid facilitating or participating in another's breach of Jewish law.
The source of this prohibition is discussed in Tosafot on Shabbat 3a and further elaborated in the Rosh. He writes: "Nevertheless, there is a prohibition, for even if a minor eats non-kosher meat, the Beit din is commanded to stop him, all the more so an adult should not assist him." This indicates that one must avoid assisting in any transgression, emphasizing the responsibility to intervene and prevent violations of the Torah.
The Avnei Nezer in Yoreh Deah 126, 3, adds a chidush based on the Tractate Shevuot, page 39a: "And if one man sins against another - a man [sins] through the sin of his brother, teaching that all of Israel are guarantors for one another."
This highlights the concept that Jews bear collective responsibility for each other's spiritual integrity. The Avnei Nezer elaborates that this obligation applies particularly when the individual being assisted is committed to observing the commandments of the Torah. However if that is not the case then it is not considered אחיך and there is no din mes’syea In such a case.
In your case unfortunately the buyer is non-religious so the above halacha of collective responsibility, won't apply.
3. The Torah commands us to fulfill the mitzvah of "Hocheach tochiach es amisecha," which entails reproving your fellow Jew when you observe them violating a mitzvah. This duty depends on whether your advice will likely be received positively, so in your case of selling a non-observant jew a ticket to fly on Shabbat, although it's uncertain how your words will be perceived, you should never the less try to approach the buyer to consider alternate dates and encourage him like by highlighting how observing the laws of Shabbat brings blessings and benefits, and through thoughtful and respectful dialogue, you may inspire a change in their heart and may even lead them toward Teshuvah.
Like this amazing story brought on the website 'Dan's Deals,' a Jewish businessman was supposed to purchase a ticket for the flight that was to travel from Malaysia to China. The travel agent, a devout observer of Jewish law, was alarmed to discover that the flight was scheduled on Shabbat, and upon realizing this – refused to conduct the transaction (this was her own decision, unlike the actual halacha brought earlier). "I'm terribly sorry," the travel agent told the Jewish client. "I cannot make this deal, as I strictly observe the Torah and commandments and make it a point not to sell tickets for flights that occur on Shabbat to Jews."
The businessman thanked the travel agent and said that he would handle the transaction himself. However, just when he was already at the airport, he decided to give up and even notified the travel agent in a surprising email which read: "Greetings from LAX airport. My boarding for the connecting flight will be in 55 minutes, and I am rethinking the plan. You were absolutely right in your decision, and I commit myself to be more considerate of religion."
The businessman informed the travel agent that he had decided to forgo the night flight from Kuala Lumpur, Malaysia to China, which was supposed to take place on Friday night, and even asked him for recommendations on where he could stay for the Shabbat meals.
A day after this news was broadcast in the global media, the Jewish client sent a message to his travel agent: "Good heavens, did you hear what happened to flight MH370? I can't stop thinking about it, it's a real miracle. You saved my life. I can't think of anything else, I don't know how to thank you”.
Wishing you well.

1. Torah: Leviticus 19:14
2. Talmud, Tractate Avoda Zora 6b.
3. Tosafot on Shabbat 3a.
4. Rosh. ibid
5. Avnei Nezer, Yoreh Deah 126.
6. Tractate Shevuot, page 39.