We use the Tax Liability field on Sales Orders, Customers, Quotes or Invoices that we do not want to be processed by Avalara at all. When Tax Liability is blank, Avalara processes the transaction. When Tax Liability is non-blank, the transaction does not get sent to Avalara at all. We use it for all our international sales (or else Avalara will charge us transaction fees to tell us that there are no US Sales Tax dues on a shipments going to countries outside US, duh).
“Tax Liability” on forms is mapped to TaxRegionCode in the database.