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.