Over-selling and backorders can be prevented by using the "Hide products that are out of stock (i.e. Don't allow backorders" checkbox in Step 4 of the offer details screen. Visit Limit the Number of Products Offered by Product Upsell to enable this feature.
Blog Posts:
- Introducing "True Upsells" for Shopify
- Problem Solved: Creating upsell BOGO offers on Shopify
- How to use cross-sells and upsells to increase revenue on Shopify
- 9 upselling techniques to explode your average order value
- How to create simple upsells on Shopify
- Why upsells AFTER checkout on Shopify will be your highest converting click