Understanding the return process

All,

we have difficulties to figure out the implemented process for customer returns in WCFM.
What we would expect:
1. Customer claims return and ships the product back to the vendor
2. on goods receipt the vendor shout trigger a refund to the customer
3. seller fee should be reduced if enabled.

Currently we have the issue that the vendor can neither set a status on returned goods receipt nor does he have any actions available (like return payment or set order status). All actions can only be taken by the admin or can be auto approved.
Even if the admin approves the return, how is the repayment triggered?

NB: In our setup all payment transactions are done between vendor and customer. The Marketplace does not handle the payment flow (due to legal limitations in our country)

Thanks for your support on this,
Stefan