They take Double Serving very seriously. If you're certain, submit. If you submit, they'll review it. Above all else, G wants to give consumers a good experience, and this policy is an important aspect of that.
At the bottom of the policy page here:
You can contact them.
Personally, I'd call support, but only if I were absolutely certain of ownership overlap, and only if the items and prices looked very similar, and only if I thought the situation was impacting my biz or my client's biz, and only if I were looked at their exact policy points, and were certain which clauses they were specifically violating. I'd lay the case out on paper first, as if I were reporting it to Google in writing - for two reasons, to send G this info once a ticket is opened, and to be precisely sure which clauses I'm accusing a competitor of violating.
Make sure you're right, make sure it's clear to you, make sure you can report a clear argument to G - before you take any action.