vendor vs customer

We have several vendors who sell our product to their clients. They purchase the product from us and resell it to their client. They pay us for the product and we give them a % of the sale as commission. How do I set these up in quickbooks, as vendors or as customers. Right now we are invoiceing them for the product and entering a bill for the amount of commission but an invoice is a customer transaction and a bill is a vendor transaction. It's important to have these transations relate;.