Scenario: A company's costs increased because of both the tarriff and some other factors (perhaps a supplier increased their prices, and the staff unionized and negotiated a salary increase, all around the same time). They probably would have eaten the cost if it was just the tarriff (who can say?), but because the total increase from all factors. was too much, they decided three months later to increase their prices to partially offset the combined loss of revenue. They then discover that sales did not drop from the increased price, so they decide to leave the prices where they are, even after the tarriffs end.

How much of the cost increase is 'because' of the tarriff? Which of their customers should they be forced to refund and how much?