You'll probably want to use a line item for the rebate up front that
reduces the amount due from customer that hits a clearing account, then
when you want to use the 'credit' have a line item for such that deducts
from the clearing account and reduce...
If you're looking to mark up materials and sell the materials directly,
you'll want to use CSP (client specific pricing) -
If you're looking for how to mark up you...