Is students' payment of a university professor's transportation fees considered ghulul (taking spoils of war before their distribution) or bribery, given the professor's unawareness of the motive?

The general rule is that it is recommended to give and accept gifts, based on the hadith: "Give gifts to each other and you will love each other," and the hadith: "If I were invited to [a meal of] a trotter, I would accept, and if a trotter were gifted to me, I would accept it."

However, a teacher is prohibited from accepting gifts from their students due to the concern that the gift might influence them to show favoritism towards the giver, except in the following cases: 1. If the gift is given after the students have graduated and the teaching relationship has ended, there is no harm in accepting it. 2. If the teaching is for an individual student, there is no possibility of distinguishing them over others. 3. If the gift is from students unknown to the teacher, there is no concern of favoritism.