The resolution order
With several rules you need a clear order. Resolution is always most specific wins:
Product rule → category rule → supplier rule → global rule
The "Calculation" column in the preview always shows which rule was actually used, so it is never a guess.
Targets are picked with real selectors: category and supplier dropdowns, or SKU/product ID for a single product — and the rules list always shows the target by name, never a bare ID.
Per-product overrides
Overrides live on the product's Cost & Margin tab and beat the rule values for that one product: its own margin/markup and its own sale margin. Landed costs and rounding are copied from the current rule when the override is created — so you don't need a whole product rule just because one product should have 55% instead of 40.
The margin floor
The floor (Pro) is a safety limit, not a rule: if a product's real margin lands below the floor, the run warns clearly. The floor is always measured against the real cost — buffers can never mask a bad deal.