student(s) complain other student(s) are sheating
This type of situation has to be handled very carefully. I've had situations where one or more students have complained about another student cheating. Often times, this "cheating" student in not part of their casual group. As an instructor, you will have to observe this student more carefully during exams. I've also made general comments in class about cheating and the expected consequences. This makes the entire class aware.
All the instructors at my school recently watched a video as part of our continual training about current methods of cheating. It is very amazing to what extent students will go to cheat. The instructor must be constantly observant for these new methods, especially in this electronic age.
I will treat all students fairly unless I observe cheating firsthand. All instructors are made aware to observe a particular student
Another way to avoid the complaint is to have your testing environment well proctored. Do not allow a student to have to tell you if a student is cheating, so you can tell one who complains, thank you and you will address the issue. (and you will already know it)