Check and Fix Sales Report

We have an oscommerce site and we have developers that list things on our site to sell. When a developer logs into their account they can view a report that lists all of their sales along with the amount of their commission. Something isn't working correctly because a developer just contacted us to let us know that her sales are showing but her total commission is not. So, something about the report isn't showing the information correctly. We need a coder that will go in and look at the report, tell us what the script means and what database table and cell each query is pointing to (so we'll know in the future) and also fix the issue. All of your work must be well commented and we'll need you to write a report detailing any database and page changes and/or additions.