How can I detect gross margin loopholes before a major promotion when coupon stacking goes wrong?

The most dangerous thing before a major e-commerce promotion isn't a lack of traffic, but rule stacking that wipes out your gross margin. Previously, when we ran weekend promotions, we had full-reduction discounts, member coupons, and bundle discounts all active at once. The test orders looked fine, but finance discovered that several SKUs were nearly selling at a loss. The problem was discount…