https://www.google.com/shopping/expr...arketingPlace:

You are eligible for promotional credit if you
(a) are new to Google Shopping Express
(b) are 18 years or older
(c) are a resident within our delivery area
(d) keep your account in good standing.
You will be charged for deliveries after the 6 month period.
You can suspend your participation in Google Shopping Express before the promotional credit amount is exhausted if you do not wish to receive additional delivery charges.
You will not be notified once the promotional credit is exhausted