Dirty data does not announce itself. It arrives quietly as blank cells, "N/A" placeholders, stray zeros, or entirely empty columns that looked fine in the source system. Left untreated, these inconsistencies silently corrupt your totals, break your relationships, and cause scheduled refreshes to fail at the worst possible moment. This guide shows you how to stop patching issues one column at a time and build a small library of reusable M functions that handle every table inco