Pull four numbers from Seller Central (Business Reports → Detail Page Sales and Traffic) and get the same first read a category manager would run: did traffic break, or did conversion? No email, no account.
The fork is simple arithmetic on your own numbers. A move of more than 10% against the comparison window counts as a real change; under that we call it flat, because normal week-to-week noise on Amazon routinely swings single digits. The branch logic and cause rankings come from our long-form diagnostic, Why Are My Amazon Sales Down?, which cites the underlying evidence: seller analyses attribute roughly 80% of sudden drops to a lost Buy Box, a dropped rank, or an uncompetitive price (Begg, 2026); stockout recovery typically takes two to four weeks (8fig, 2026); and negative reviews move sales more than positive ones (Chevalier & Mayzlin, 2006).
The revenue gap estimate is your own data multiplied through: units = sessions × conversion, and the gap is the difference in units between the two windows at your average selling price. It is a description of what already changed, not a forecast.