In Arborgold both the Customer and the Service must be set to "Taxable" in order for tax to calculate. Here's how to set that up.
IMPORTANT: Both the service and customer must be set to taxable.
Prerequisite: You will need to set up at least one Sales Tax Rate
Create or Edit Sales Tax Rates
Add Tax Level to Customer Profile
Set up Sales Tax Rates
Gear Icon
List
All Lists
Accounting (bottom)
Sales Tax
Select Add New from the top right
Add Tax Name (i.e. city, county, state name)
Add percentage (this is entered as a whole number - 7 = .07, 8.7 = .087)
Add Vendor (this is used in Quickbooks so if you export to Quickbooks you will need to ensure these match)

Add Tax Level to Customer Profile
Add a new customer or select a customer to edit
Go to Account Information/AR
Select the appropriate tax level from the drop down

Set Default Tax Level
If set each new customer created will have this tax level set but it can be overridden
Gear Icon in the top right
Company
Defaults
Under New Customer Defaults
Default Tax Level
Use Drop down menu to select most frequently used tax setting
Save

Set Services as Taxable
Gear Icon in the top right
Items
Services
Double Click Service to update
Select check box for Taxable setting
Check is taxable
No check is non-taxable
