A compatibility rule can protect a customer from ordering two items that will not work together. It can also create a new problem when it stops a perfectly valid basket. WooCommerce incompatible products need more than a red warning and a hopeful assumption that the catalogue is correct. They need a small, testable decision: what combination is genuinely unsuitable, what exception makes it acceptable, and what should the shopper do next?
This guide takes a quality-assurance angle. It is for the merchant who has identified a real conflict, but wants to launch the rule without trapping customers, hiding the remedy or sending support a fresh batch of avoidable questions.