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Ohio has actually passed a law that regulates access to retail establishment restrooms. Here is the actual text of the law:
"Any retail establishment that has a toilet facility for its employees is encouraged to permit a customer to use that facility during normal business hours if the toilet facility is reasonably safe and all of the following conditions are met:
(1) The customer requesting the use of the employee toilet facility suffers from an eligible medical condition or utilizes an ostomy device.
(2) The employee toilet facility is not located in an area where providing access would create an obvious health or safety risk to the customer or an obvious security risk to the retail establishment.
(3) A public restroom or employee restroom normally available to the public is not immediately accessible to the customer."
(Title 41 Chapter 4173.02)
Summarized for your purposes, a retail establishment should let you use their restroom if you are a customer and the restroom is normally made available to the public. If you are simply "waiting" on the business's premises, you would not be a "customer" and therefore probably would not be entitled to use their restroom. But if you buy something, then you can argue that the law entitles you to use of their restroom facilities.
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