I think it's shady to use cross-shop information unless the customer explicitly opts into it.

But shopify isn't just a payment processing service. It's a full blown ecommerce suite. Do you think there's an online store out there that gets rid of all PII once an order is paid for, or even after its fulfilled?

We've had people try to return/replace things (or even credit card disputes) years after they bought it. How exactly would that work if we got rid of all information about their order shortly after they made it?