Hello, @Cellist.

Allow me to join the conversation and share a few details about the report. 

You don’t have to select a range of cells to get the grand total of all items sold. It should be available at the bottom of the Sales by Product Service/Detail Report.

I’m including a screenshot of where it should be after exporting it to Excel.

That should do it. Please let me know if you need anything else. I’ll be more than happy to help. Have a good one!