Hi,
I have another suggestions
1. Please modify customer-vendor communication become 3 way communication user - vendor -admin. For example, similar like Ebay message: inbox: compose, send and trash. Ebay inbox has 3 way communication message that filter between customer - vendor, admin-customer, admin-vendor.
2. Resolution center addon is also 3 ways communication but this one is for the problem with order, item or vendor; Customer complaint by creating a ticket to ask vendor solve it. If the ticket is not solved within a period, it escalate to admin.
3. Maybe, integrating 1 and 2 into a support/helpdesk
This would be a awesome and complete to your multi vendor script. We will be happy to buy it.
Thank you