According to Google Shopping policies, what would cause the disapproval of individual items or an entire Merchant Center account?
Unsecure checkout or a missing refund policy
Sale of gambling related products such as poker chips
A product URL that links directly to only one relevant item
Products with an availability attribute of out of stock
Google’s goal is to provide the best user experience on Google Shopping. In order to ensure that the ads Google show to online shoppers are safe, secure, and comply with legal requirements, Google maintain comprehensive enforcement of the Google Shopping policies for all merchants.
Read more here: https://support.google.com/adwords/answer/6103800