OSCommerce Modification - Charge vs. Auth

I have a version of OSCommerce with a calculator that allows people to figure out how much their item is worth. From there, they can choose to sell or trade in for an item in the shopping cart. If someone is simply buying an item, the credit card should be charged (it already does this - the processor is all setup) but if someone is trading, the credit card transaction should partially only be set to authorization. Put very simply, its like this: buying an item WITH A TRADE, CHARGE the invoice amount (total minus trade credit) AND run an AUTHORIZATION (this is not a charge but a hold on funds and the right to charge in the future) for the AMOUNT OF THE TRADE CREDIT. Example I am buying a new item for 299 I am trading an item for 60 credit shipping is 10 total CHARGED to me is $299 - $60 + $10 = $249 total AUTHORIZED on my card separately is $60.00 Everything works currently - I just need to have it authorized only on the part of the payment that is from a trade. ## Deliverables 1) Complete and fully-functional working program(s) in executable form as well as complete source code of all work done. 2) Deliverables must be in ready-to-run condition, as follows (depending on the nature of the deliverables): a) For web sites or other server-side deliverables intended to only ever exist in one place in the Buyer's environment--Deliverables must be installed by the Seller in ready-to-run condition in the Buyer's environment. b) For all others including desktop software or software the buyer intends to distribute: A software installation package that will install the software in ready-to-run condition on the platform(s) specified in this bid request. 3) All deliverables will be considered "work made for hire" under U.S. Copyright law. Buyer will receive exclusive and complete copyrights to all work purchased. (No GPL, GNU, 3rd party components, etc. unless all copyright ramifications are explained AND AGREED TO by the buyer on the site per the coder's Seller Legal Agreement). ## Platform linux