SUM totals from journal entries based on content of previous cell

I am having a hard time figuring out how to describe my problem, so I've attached an example to refer to.

I am entering the Sales Reps names via a drop down list on a sheet titled 'Commissions'. I want cell B3 on 'Commissions' to add up all the coordinating totals for that sales rep from sheet 'Sales'. There is no designated number of items that I can use the regular OFFSET (some orders will have one item, some will have ten) to count down to the total cell based on searching for Sales Rep. Basically, I want to be able to sum the totals, based on if the most immediate "Sales Rep: " cell above that total has the Sales Rep name in it that I enter into cell B1 on 'Commissions'.

I would also love to be able to deduct any cells (Line Price) that say "Setup" in the Product description from the totals for that rep, but I may be able to figure that out myself.

Any help or guidance would be most appreciated! Thanks.

I'm going to say it before anyone else does. This should really be in a database or at the very least set up in a table format. That said. I am still interested to see if anyone can figure out how to match the sales person to their totals.

Thanks for the input. Unfortunately, I am working with a report that's generated from my company's website into a CSV or XLSX file, and so I don't really have any flexibility in how the data is reported or arranged.