Hi, I am currently in Varanasi taking private Hindi classes with a teacher called Binit Kumar Mishra. I tried to do as much online research as possible before choosing my teacher and found surprisingly little information, so would just like to give my two cents and say that if anyone is thinking of taking Hindi classes while in Varanasi (whether it be a few days or a few weeks) then I would highly recommend Binit.
Binit is friendly and welcoming and his classes are focused and individually tailored - three weeks ago I couldn't speak a word of Hindi and now I can even read and write simple phrases in Devangari script! He is also very flexible and accomodating of your timetable, and is never late to a class.
I am still studying with Binit and am so pleased I chose to study with him - you can contact him by visiting his website www.hinditeachervaranasi.com.
I hope my experience helps anyone else thinking of studying Hindi in Varanasi.