Recording credit received instead of commission

I have a vendor that I resale their products without ever taking possession of the products.  All my orders are drop shipped to the customer.  The customer PO normally comes directly to me and then I send the Vendor my PO.  There have been a handful of customer PO's that are addressed directly to the Vendor in the transition from customers ordering direct from them and now ordering from me.  With these particular PO's I still get my commission portion (normally my profit from sales).  The difference is instead of writing me a check they are just giving me a credit for my portion of the profit as a credit toward my account since I have other invoices to pay them.  I know how to create a credit memo and apply it to other invoices.  What I don't know is the category to code the credit to.  It is technically income for me.