Duplicate SKU

The obvious cost is a longer product list. The real costs are downstream. Inventory splits, so a style that has six units on hand reads as four and two and triggers a reorder it does not need. Sell-through fragments, so a strong seller looks average twice over. Reordering compounds the error, because the buyer is reading numbers that describe half a product each.

Cleanup is also expensive in a way creation is not. Merging two records means reconciling two stock counts, two sales histories and any open purchase orders pointing at either one.

Almost always at receiving, and almost always by a document that could not be reconciled to an existing record. A colour code that did not match, a style number formatted differently from last season, a size label written another way. Each near miss produces a new record rather than a match, and the catalog grows a twin.

Two variants of the same style in different colours are not duplicates; they are the structure working correctly. Neither is the same style carried under two vendors at different costs, if you genuinely buy it both ways. Merging either of those destroys real information, which is why detection should always be followed by review rather than a bulk operation.

Prior-season carryover is the case most often mistaken for a duplicate. A style you bought last year and again this year, with a changed style number but the same colour and size, may legitimately be two records if you need to report on them separately, or one record if you do not. That is a merchandising decision rather than a data-quality one, and it should be made deliberately instead of resolved by a detection script.