Do you ALWAYS use the median multiple of a set of public company comparables or precedent transactions?

There’s no “rule” that you have to do this, but in most cases you do because you want to use values from the middle range of the set. But if the company you’re valuing is distressed, is not performing well, or is at a competitive disadvantage, you might use the 25th percentile or something in the lower range instead – and vice versa if it’s doing well.