What is the ruling on lending cooking utensils to girls who exchange meal coupons for food of unequal value, especially given that a doctor of Sharia described this exchange as "excessive exploitation" (al-ghabn al-fāḥish)?

If the university takes financial compensation for the coupons, then it is not permissible to exchange the designated food before taking possession of it. However, if the coupons are a gift from the university, then the matter is different. Possession of the meals occurs when the students are present in the university restaurant and the food is presented to them. It is permissible to exchange a known meal for juice or fruit. If the substitute is of lesser value, the student has no choice as long as she knows the value of each when selling or exchanging. There is no harm in the questioner lending cooking utensils to her colleagues who exchange food, and it has no relation to the exchange.