I also use Avalara and I have to check every single invoice to make sure that the automatic calculation is turned off and the AvaTax is turned on.  It has added a time-consuming step to my invoicing process that I didn't need.  I have asked and there is apparently no way to make the AvaTax calculation the default sales tax calculator.  So I googled "disable Quickbooks automatic tax calculation" and found this thread of misery.