Hi all,
I am using ZC 1.3.5 and am trying to understand which files are used when calculating shipping for the following purpose:

If a customer buys from Manufacturer A, shipping is by UPS and has the option of Ground, 3day, 2day, or nextday
If a customer buys from Manufacturer B, shipping is Flat Rate and UPS should not be shown
If a customer buys from Manufacturer A+B, then shipping is Flat Rate, but the handling charge increases, and UPS should not be shown.

Which of the ZC catalog files do I need to modify to allow me to write this logic?

Is there an easy way to see which Manufacturer are included in an order?