The sale model

Three questions, three answers

• WHAT discount? The rule. Every rule can carry a "Sale price value" — e.g. regular margin 40%, sale margin 20%. The sale price runs through exactly the same chain as the regular price, just with the sale margin.
• WHICH products? The flag. A checkbox on the product's Cost & Margin tab, or an on_sale column (yes/no) in the import file for bulk. Only flagged products get a sale price.
• WHEN? WooCommerce's normal date fields. sale_start/sale_end in the import file fill Woo's own schedule dates — no parallel date system.

You always win

If you type a sale price into Woo's field yourself, the plugin recognizes the sale as yours and leaves the product entirely alone — regardless of flags and rules — until you remove the price. The plugin only ever manages sale prices it wrote itself.

Sales that follow the cost

Because the sale price is margin-based, it is recalculated when the purchase price changes — a sale never quietly sells at a loss.

The Sales page

Cost & Margin → Sales lists every plugin-managed sale with product, price and dates. "End sale" closes one, "End ALL" closes all — journaled and undoable like everything else.