Where can I submit a bug for the Play Store or Google Play Services?

I don't know exactly where the bug lies, I think it is on the Play Store but I guess it could be Google Play Services.

Basically a user with accounts X and Y on their phone will make an in-app purchase on my app with account X. Then I will do a staged rollout of an update and that user who had the app installed as account X all of the sudden will get the update for account Y and the app will not recognize the in-app item as purchased.

I have talked with another developer with a similar in-app model and they experience the same bug.

Where do I submit that bug?

How do I contact Google Play Store?

5. Online Assistance and Customer Care. To view your Google Play balance, visit https://play.google.com/store/account. To speak to customer care, call us at 1-855-466-4438.

Yes, currently at the bottom of https://support.google.com/googleplay/community one can post issues.

If you think it is a bug. You create an issue in the issues tracker. The proper person from Google team will look into your issue there, and will check if it really is a bug or not.