I’m using a spreadsheet that flags items if they haven’t sold for X days, but it doesn’t catch SKUs that have never sold since the STK report I use doesn’t include unsold units.
A common approach is to start from your full catalog rather than sales reports, using the Manage Inventory or FBA Inventory reports as the master list and then layering sales data on top of that, because this captures SKUs with zero sales as well as slow movers.
Many sellers export the Inventory Ledger, All Listings, or FBA Inventory Age report and then use a lookup or pivot against Orders or Business Reports to flag SKUs with no sales history at all, which avoids relying on tools that only show sold units.
If you want something more automated, tools like STK, Seller Central’s Inventory Performance dashboards, or third-party inventory analytics can be combined with a simple rule such as “no sales since listing date” or “no sales in 30/60/90 days,” including zero-sale SKUs.