Can a contact be both a supplier and a customer

I have a way around what you can do about this, user, User45774.

At the moment, providing both supplier and customer as a contact isn't possible. This will cause conflict in the system especially when assigning transactions that will result in duplicates.

Instead, you can enter the same customer and vendor name and add a character that will show a slight difference from each other to avoid errors and be able for the system to correctly detect each transaction created.

As an example, you can add Mary as a customer, and then create Mary1 as a vendor.

On top of that, QuickBooks Online (QBO) provides a variety of reports that cater to your business needs. You'll only have to customise them to ensure you'll get the data you need. For more information, read this article for datails: Customise Reports in QuickBooks Online.

Feel free to let me know if you have any other concerns with your supplier or customer. We'll always be right here if you need further assistance.