After having done a full implementation of nationwide sales tax collecting and reporting utilizing Avalara in AC9, there are a number of improvements AC9 needs to make it feasible for a merchant:

Order Recalculation
While it was just recently added that Avalara gets updated when an order is recalculated, the admin should not be required to initiate the recalc in the first place. Order recalc should be automatically done at every touch point where the order can be changed. This includes editing the shipping address, edit/delete line items and adding line items.

Doing this ensures that Avalara transactions are always in sync the AC9 orders. Not doing this leaves the door open for massive user error that costs real cash from the merchant's pocket.

Order Recalc Sequence
Already discussed in forum post but needs mentioning here. Taxes should always be the last thing calculated, because other components of an order (ex shipping) can be considered taxable. You don't want to calculate taxes, then calculate shipping, because a change in the shipping charge could easily result in a different sales tax amount.

Discounts Recalculation
This has never been written and I'm shocked nobody has ever brought it up in 15 years. If the store has a volume discount rule that kicks in at qty 10, editing an existing order item qty 5 to qty 15 will not automatically invoke the quantity discount for the order. Discounts need to be included in order recalculation.

Tax Exemption By Province
A B2B business can easily have a customer that ships to different states. So while the B2B business may be tax exempt in Georgia, they're shipping an order to Florida where they are taxable. A single 'tax exemption type' at the user level no longer works. AC9 needs the ability to specify all the tax exemption attributes by state/province at the user level. In addition, Avalara wants to know tax-exempt start date and tax-exempt expire date for each tax exemption definition. There is no provision for any of this in AC9 today.

Exemptions Import
In the internet sales tax world, there is a collective group of US states that are known as 'SST' states. These states all agree to operate and remit internet sales tax through a common set of onboarding forms and tax remit forms. For orders shipping to these SST states, Avalara will ignore the TaxExemptionType value sent via the API. For the customer to be tax-exempt, that customer must already be set up within Avalara itself as tax-exempt and have a tax exempt certificate on file. There is no API to electronically register these tax-exempt customers in Avalara. But there is an import page. AC9 needs a way to generate an export file (Excel format) that can be imported on a regular basis into Avalara.

Not all US states are a part of the SST program. Avalara does not require this customer setup within Avalara for states that are not a part of SST. For non-SST states the value of TaxExemptionType sent via the API is respected.

Order Exemption Type
There is no mechanism to change the order tax exemption type. This is sorely needed for customers who placed an order as taxable, but submit their tax exemption prior to filling the order. The current Recalculate feature populates the order TaxExemptionType value, not the order user's current TaxExemptionType.

Avalara Transaction ID
The design of storing the Avatax document ID in the sku of the tax line item is terribly flawed. If the tax line item is ever deleted by the admin user, the connection between the AC9 order and the Avatax transaction is permanently broken. Ideally the Delete button should be disabled on the Items tab for items that have the Avatax ID on them.

Onboarding Avalara Transaction Import
It would immensely helpful to provide an export routine that dumps Able order data (by date range) into Avalara's transaction import file format. This allows a merchant to onboard with Avalara, import YTD sales data and then know exactly where they stand with nexus thresholds in every state. Otherwise the merchant will easily draw attention to themselves at the state level and risk a state demand for tax audit. State tax auditors are looking for merchants like that because it's free money for the state. And it's hard cash right out of the merchants pocket if the merchant winds up on their radar.

We did extensive customizations to a Gold R9 site for Avalara and one big one was that the tax had to be calculated on the shipment and not the order because the order could have several shipments. Also, the commit happened when the shipment was shipped, not when the order was placed. Maybe 9.0.6 already has some of this.