If you have a vendor that is also a customer and you want to do a trade between the two then youll want to be sure you have a vendor file and customer file created for them.

Make sure you write down the Vendor ID then youll go into the customer file, F9-More, put the Vendor ID in the Vendor Code for Warranties.

Then youll go back to the main customer file screen and do a F12-Credit, enter in your memo, in the amount of credit you will enter what will be posted to their payables as a credit, then apply to invoices, process. The system will then prompt, "Would you like to credit payables for vendor?" select yes then allow system to process through now when going over to the payables side you will see a credit sitting on their open screen and ready to be applied to any open invoices by selecting P to pay.