You could, or you could bake it into your vendor commission or subscription rate. But if you want them to basically bid on position, then you'll need something more dynamic.
Thanks for that. On the subject of subscriptions, I notice that CS-CART multi-vendor does not force vendors to a payment gateway to pay for annual subscription fees or an up-front fee, nor provides any integration with a gateway for this. The transaction fee is dealt with by Stripe etc, but not the annual fee. It just shows as a negative balance on their account. How are other marketplaces getting their vendors to pay for this up-front fee?
Actually, I'll ask this publically as a new topic.