Q. I am in the store on Chol Hamoed and there is a lady (I do not know whether or not she is Jewish) who asks me to pass her the bagels on the top shelf because she can’t reach them.
Am I allowed to pass them to her?

1. Is this called benefiting from chametz?
2. Is this lifnei iver? Assisting someone to do an aveira? [In the event that she is Jewish]

A. In question 63 in regards to a nurse serving during Chol-Hamoed Pesach meals that contain chometz to non-Jewish patients. we wrote; It is forbidden for a Jewish nurse to prepare or serve meals that contain chometz during Pesach, even to non-Jewish patients. There are a number of prohibitions involved, such as “Mistaker B’isurei Hanoe” or deriving benefit from proscribed items and desiring their existence (O.H..450, 4 – Mishna.Berura. 9), Also we should be concerned that the chometz may be eaten or tasted during the process (Mishna Berura ibid. 21). Poiskim recommend that somebody whose occupation requires the handling or providing of chometz food, should ask for a substitute during Pesach or engage in a different task. (Igros Moishe C.M. 4, Yesodei Yeshurun 6, p. 207, Chashukei Chemed, Pesochim p. 190, see also Teshuvos Vehanhogos O.H. 299).
Similarly, on question 65 in regards to a Jewish patient transferring a tray of chometz food to another non-Jewish patient, laying in the next bed, during Pesach, Horav Shlomo Miller’s Shlit”a opinion is that it is prohibited, as the non-Jewish patient will remain grateful for the favor done, and that constitutes a prohibited benefit of hometz. He may also transgress in the desire of the existence and being (Roitze Bekiyumoi) of this particular chometz, since he will be careful not to tip the tray and spill the food. (O.C. 450 – Chashukei Chemed, Pesochim p. 190).
The prohibition of “Lifnei Iver” or “Placing a stumbling block before the blind” is interpreted by our sages as: facilitating or helping others commit a Torah violation. (Talmud Avoda Zarah 6b) This prohibition is codified in Shulchan Aruch in several places such as Y.D. 148:5 pertaining the assisting of a Gentile in committing idolatry and in Y.D. 240:20 in regards to a father’s proscription of physically chastising older children, as this will only entice them to hit back, resulting in a capital offense. Tosafos, Ramban and Ran (ibid.) and other Poiskim, are of the opinion that this prohibition is limited to cases where the recipient is unable to transgress without the giver’s assistance. If, however, the idolater could reach the item independently, then one may hand it to him despite the certainty of the ensuing violation. In your particular case, the person assisted can easily get to the chometz by other means such as asking another Gentile customer or an attendant for help. (See Mishne Lemelech – H. Malve 4: 2, Chavas Yair 185, et. al.). Horav Shlomo Miller Shlit”a pointed out that the opinion of HaGra (Y.D. 151: 8) is that even when it can be done easily by others, there is still a “Lifnei Iver” prohibition
However as Tosafos (Shabbos 3a) and Shach (Y.D.151:6) mention, there is a discrete rabbinical prohibition against helping one violate Mitzvos, called “mesayea lidvar aveiro” (“helping someone commit a sin”). Igrois Moishe (Y.D. 1,72) deals with the question of mesayea when someone would perform the transgression nonetheless. (See question 207).

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a