Cross-sells work, upsells backfire

There's a meaningful difference between "add a case for $15" and "upgrade to the Pro model for $200 more." The first adds to the purchase. The second reopens the purchase decision.

Cross-sells work because they don't challenge the original choice. You already decided to buy the phone. A screen protector is a small addition that complements it. The decision is easy: yes or no, either way you're still buying the phone.

Upsells introduce doubt. "Maybe I should get the better one?" Now you're comparing products again. The decision you already made is back on the table. Some people upgrade. Many more abandon the cart entirely because you turned a done deal into an open question.

Keep cart-page suggestions under 25% of the original item's price. Position them as additions, not alternatives. "Goes well with" is better than "Consider upgrading to." The first says "you made a great choice, here's more." The second says "maybe your choice wasn't good enough."