You see the field for assigning that a Purchase is directly related to the customer, on the check expense, bill and credit card charge entry, which is called Job Tracking = you just assigned that cost. That's how P&L by Custome, P&l for one Customer Filter, and Customer Income summary reporting all get their Direct Cost  data = you need to assign it on the entry when that purchase is made that is Direct. Example: I enter that I just bought doors and windows for your garage. Even if I charge you a Fixed Contract Fee as my revenue, I also Track those purchases as related to your project. Now I have COGS data for You.