Sort Sales Report by Total Sales per Parent or Top Level Customer

Answer: 

A. If all customers have parent-child relationship:

1. On the Sales by Customer Report > Navigate to Edit columns, remove the Customer column
2. Replace the Customer column by going to Customer/Job folder > Parent Customer/Job > Name. Then Group=checked
3. Go to Sorting. Then on the Add Fields section > Expand the Sales folder > Transaction Total (Revenue). Check Descending
4. Save the report

B. If NOT all customers have parent-child relationship:

The solution above will not apply if there are customers without sub-customers. These customers will actually be excluded in the report if you follow the steps above.

Follow these steps instead:

1. Navigate to Lists > Search > Saved Searches > New
2. Choose Transaction as the Search Type
3. Under the Criteria tab, set the following filters:
 * Type is any of Cash Sale, Invoice, Credit Memo
* Date is within this fiscal year  
* Main Line is true
 4. Under the Results tab, set the following fields:
 * Customer Fields... Top Level Parent (Summary Type: Group)
* Amount (Summary Type: Sum)
 Sort By: Amount ; Descending=Yes
5. Assign a name for the search
 6. Save and Run