The campaign matching algorithm always works the following way:
http://support.qualityunit.com/063458-Campaign-matching-algorithmSo, if in campaign X (with 0% commission) I define the product ID of "red car" and someone makes a purchase of 'red car' then it will immediately match campaign X and there will no commission generated for that purchase, more exactly, it won't be even tracked , unless the "Save transaction with zero commission" is checked in the particular campaign's commission settings.