Hello, @CBPP. I appreciate the efforts you've made. I'm here to share additional information about your issue.

Sales Tax Liability report summarizes your taxable and non-taxable sales and the total sales tax you collected from customers. The Sales by Customer Summary Detail report lets you see the total sales made for the specific period.

The reason why Sales Tax Liability Report and Sales by Product and Services Report are different due to various reasons like the following:

• The report has a separate report basis. Businesses that use an accrual basis often pay sales tax on a cash basis. 
• Reports have different date ranges. 
• Finance and statements charges will not appear on the Sales Tax Liability report. 
• Reimbursed expenses may or may not appear on these reports, depending on how they've been set up.

When you pass on expenses to a customer during a sales transaction, you don't need to use a sales item. However, reimbursed expenses won't appear in standard sales reports that are filtered for all sales items. These transactions are usually taxable, so their amount should be included in the sales figures for the Sales Tax Liability report.

Also, you can check this article if you want to remember its current customization settings: Memorize reports in QuickBooks Online.

Don't hesitate to get back to us if you have further questions about reports in QBO. We're always available to assist you.