Take a store where about 20% of orders come back within 30 days. If you import gross purchase revenue, Smart Bidding is learning from money the store never keeps, and it will chase categories with high return rates, sizing-heavy apparel being the classic example.
People usually split into two camps. One says send gross order value, because that's what the customer actually paid and changing it creates a mismatch with what finance sees. The other says net out refunds and cancellations, either through conversion value rules or a daily offline import, so the bidding model stops overvaluing returnable products.
I lean toward netting returns out, but only when the return rate is high and stable enough to matter. Below that, the reconciliation work probably isn't worth the effort. The harder case is when return rates swing a lot between product lines. How do you handle that?