I think that studying teachers' behaviours through students' perceptions is not a good way, as there are many biases that could influence it. However, I have not found much literature on the subject. Do you know of any interesting reviews?
If possible I would always opt for observer ratings or ratings of video recordings. However, there are many studies that applied student perceptions as an indicator for teaching quality. So, that is absolutely ok too and can easily be argued for. In the end it is definitely also more economical. I don t know of any reviews but could let you know of some studies that used it. Maybe this direct comparison study is a good start:
Article Validity and reliability of student perceptions of teaching ...
It should be one of the factors. The teaching quality should be assessed through a thorough process involving departmental faculty, students, and contribution to research.
Your question is of great interest. I have always been evaluated as a Faculty Member from the very first semester I worked at the University. Honestly, at first, I felt uncomfortable, but over time, I have had to get used to it. Also, I have read about this topic. In fact, there are quite a few publications about it. And some of them confirmed my predictions. It has been observed that when students evaluate their teachers, it results in an inflation of students' grades (between 10 and 20%). The reason is that, how is it possible to maintain a certain level of demand for the students when they evaluate you, and therefore, critical aspects for the Faculty Member such as the working contract renewal, salary increase, or promotion depend on that? Do students have the proper knowledge to evaluate the teacher, or do they evaluate him/her based on the grades they obtained in their assessments, or based on their teachers' sympathy or preconceived image? Isn't there a risk that with this system, teachers, due to the fear of obtaining a low grade, will artificially increase their students' grades? And, if so, getting a high score from the students means being a good teacher, or on the contrary, a teacher who lowers the academic standards so that the students can obtain good grades without making enough effort to acquire the knowledge stated in the course syllabus. Nowadays, there is an obsessive tendency to measure, quantify, compare, and rank all processes in the educational field and other sectors. And perhaps, it is not easy to do so in the education sector. Or maybe, it is not done with the appropriate assessment instruments. It is true that students are the ones who spend more time with the teachers. However, I doubt that teachers' evaluation made by the students positively impacts the teaching-learning process.
I actually disagree, unfortunately, with some who suggest this is a valid and adequate measure. My experience is that the students' opinions sometimes are very biased and hence, less reliable. It seems these reflections can be very reliant on perceptions and not giving adequate credit of teachers who ask difficult questions to stimulate students' intellectual growth but the students feel this is oppressive and maybe even unfair.