If you're unable to process a refund, it's likely because your user account doesn't have the necessary access permissions. The merchant has the ability to grant these permissions to users as they see fit.
As for some refund options appearing greyed out, this is usually because the original payment method doesn't support refunds. For instance, if a customer paid in cash, it's not possible to refund to a credit card. Refunds can only be processed using the original payment method or via a credit voucher.
This is in compliance with standard regulations.