According to Neil Patel (read blog post):
- If you have very low conversion rates everywhere, then try to optimize that first.
- However, if you have a low conversion rate on your checkout page, then put it only in your product pages (or in any other part where you don’t have low conversion rates).
- If you have high conversion rates in one of your checkout steps, test putting it there.
- If you see an increase in your average order value (among other important metrics such as revenue), and at the same time you don’t see a decrease in your conversion rates, keep it.
- If not, keep testing until you find the right place for your upsells.
Here are a couple of Shopify Apps: