How do I know if my Customer is shopping from an Unincorporated area?

I am trying to figure out how to tax people who buy furniture from me online. Washington State uses the destination of the product to determine sales tax. How am I supposed to know if a customer is buying from an unincorporated area or not? I understand I only have to tax those who live in WA. but people shop by state,city, zip, not county. or zone code.How do I know if my Customer is shopping from an Unincorporated area?
their address is the one you use to determine what sales tax rate to charge

of course you have no way of knowing if their area is incorporated or not, and you don't need to

their address is sufficientHow do I know if my Customer is shopping from an Unincorporated area?
Looks like the state will help you figure this all out:



destinationtax.dor.wa.gov