How to verify that guest email is already exist as customer in system on checkout page in Shopify

Question

We need to add feature in Shopify that guest/customer can't purchase the product more then limit defined in product meta field in CMS.

Basically, we have limited edition of product so want that single person [email verification] can purchase 1-2 quantity in life time. For this we tried following ways:

Webhook: But not able to find solution to show error on checkout page and stop order if we found such condition.

Custom code on template itself: But we are not able to verify email from CMS that its already attached to a customer otherwise we will get all orders of that customers and then products and matched with current cart product and show error message

Answer 1

Don't allow guest checkouts. Force your customers to login with an email. Them you can be certain of not allowing them to checkout with more than the one or two of these products in their lifetime. Otherwise, accept their order and simply cancel/refund the cheaters.