1. Opened or damaged packaging
The commonest and the least dramatic. Packaging that arrived crushed, was opened to verify contents and never restored, or is simply not robust enough for the journey it makes.
Test the packaging standard against the route, not against the warehouse. A box that survives a pallet and fails a single-unit dispatch is a real finding and a fixable one. Where the wrong product arrived rather than a mishandled one, the lane is wrong item complaints.