See[0]. The "Pay With Google" initiative is adding a 'supportedMethods' of 'https://google.com/pay'. What is then in the data section of that supportMethods call to Google is up to Google, which is specified here[1]. It looks like Google required "merchantId", which the merchant registers with Google to get access to the cards Google has stored for that customer.
So yes, if a merchant wants to use a customer's card on-file with Google to pay at a merchant with "Pay with Google", Google will be able to connect the 2 dots together, but I'd read the ToS to see what is allowed[2].
The value-add here for merchants is to get customers to complete a purchase without having to go through the pain of typing in their card details. And for consumers, if they don't fully trust the website and the website is using Gateway Tokenization, then the merchant never sees the credit card data.
So yes, if a merchant wants to use a customer's card on-file with Google to pay at a merchant with "Pay with Google", Google will be able to connect the 2 dots together, but I'd read the ToS to see what is allowed[2].
The value-add here for merchants is to get customers to complete a purchase without having to go through the pain of typing in their card details. And for consumers, if they don't fully trust the website and the website is using Gateway Tokenization, then the merchant never sees the credit card data.
[0] https://www.w3.org/TR/payment-request/#the-methoddata-argume...
[1] https://developers.google.com/payments/mobile-web-tutorial#a...
[2] https://payments.developers.google.com/terms/sellertos