A post-purchase upsell that worked for us was using our CRM to send personalized emails that matched each customer's interests, reminded them of past purchases, and suggested tailored products. It was effective because it felt relevant to the buyer and led to more reviews, more reorders, and stronger customer relationships. I recommend starting with simple segmentation in your CRM and a follow-up email that suggests complementary items to the last order.
My favourite tactic is the one-click upsell occurring directly in between the actual checkout confirmation and thank you page. It's a psychological 'sweet spot' whereby the customer has 'signed on' to the brand, but before the inevitable 'buying high' fades, you offer a complementary product (usually discounted accessories or 'refills'), all without the customer needing to enter the credit card number again! What makes it work is total lack of friction. Too many Shopify merchants upsell inside the cart or checkout flow, leaving buyers paralyzed and resulting in checkout 'dropouts'. Moving the offer post purchase keeps your primary package sale intact whilst adding another secondary offer with absolutely zero risk to your original close. Whenever we try this, provided the upsell is a 'no brain' extension of the first purchase, we see conversions land between 10-15%! For first timers, I always suggest trying the 'Frequently Bought Together item' at a very low 15% discount, which is easy for the shopper to understand and get value from and is safest to dip a toe into the water at which bite to increase purchasers' original bounty with something the original buyer probably forgot to purchase. All too easy to get sidetracked on the hunt for traffic, but sustainable growth lies in the precious few seconds after the entrance of actual buyers' credit card numbers.
A post-purchase upsell that worked exceptionally well for us used Klaviyo to segment recent buyers by product category purchase history and anticipated next purchase dates, then send tailored follow-up offers. It was effective because Klaviyo’s data science driven predictions and native Shopify integration made precise targeting and automation straightforward. If you’re starting out, set up those two segments in Klaviyo first and build a simple post-purchase flow around them.