AbleCommerce Shopping Cart Software

What fields are used to calculate shipping using the Shipping Estimate in Gold?
It seems like having both state and zip code fields are not necessary.

Could the zip code field be safely removed from the Shipping Estimate? (or the state field? Which is the better field to remove?)

For domestic shipping, you will need the zip code. For international shipping, you need the state/province and country depending on the shipper. eg. the USPS only uses country.

For domestic shipping, when I enter a fake zip code (12345), the shipping estimate still returns shipping methods and charges.
This leads me to believe the zip code isn't being used. Why is zip code required?

Your fake zip code is for Schenectady, NY 12345

If the state is Washington and the zip code is 12345, then which shipping methods will show? Shipping for Washington or shipping for New York?
When I've tested this, the shipping shows for Washington and the zip code is ignored.

One thing you can try is to enable debug for your shipping provider. Use the estimate form and then find the log file in the \app_data\logs\ folder. Open it up and look at the information being sent to the service and what is being returned. It will probably shed some light on the issue you are having...although I'm still not sure what you're having trouble with.

If the zip code entered and the state entered are mismatched (not in the same state), then it uses the state and ignores the zip code.
Why is zip code required if it isn't being used?

This is just a guess, but:

if
they are mismatched, and the user is not asked to correct them
then
one of them has to be used, and users are probably more likely to have typed the zip code incorrectly than the state

Remember there are multiple shipping gateways and the requirements are likely different gateway to gateway. The estimator is designed to work with them all, but you may be able to make it simpler for just one gateway.