[mrala]

Since the article doesn’t mention it, CPA stands for cost per action.

[closewith]

Cost Per Acquisition (of a new customer).

[amelius]

How do they know if the customer is new or not?

[closewith]

Normally in e-commerce, it's based on email or phone number. In physical retail, they use all sorts of tactics, from loyalty cards to facial recognition (where legal, which it shouldn't be).

[HEGalloway]

tracking via cookies (that expire after X days) or some kind of identifier in the CRM