On my course, there were definitely lecturers that were known as being harsh markers and thus sometimes people avoided taking their modules if possible. Although one of the second-year courses is taught by one of these harsh markers, and it is among the most popular courses from year to year regardless, so people obviously aren't too put off if the module itself covers good material. I never deliberately avoided a course, in fact I took two courses with one of those hard markers and was fine - I just worked harder!