Commision

Hye, I want to use this product for my marketplace but need to find out if there is a way to get commission from the shipping fee of my vendors sales? The reason is because with my payment gateway, I (the site owner) am paying a percentage on the total value of every credit card transaction… So if a person buys a product for $100 and there is a $10 fee for shipping by the vendor… I will be paying a percentage of $110 to my payment gateway for credit card processing… Not just a percentage from the $100… I hope what I explained was clear enough to be understood… I look forward to your reply…