How to handle returns for service?

We don't have many returns from customers where we issue a refund.  What we do have is customer's sending in their product for service, upgrading, etc.

I'm trying to find out how to use NetSuite to handle this.  Sometimes the service or upgrade results in an invoice being generated.  The RMA system has some of the features that I like and I would like to have something like that for servicing a customer's product.

Would cases would be useful for this?  I haven't used them much, I haven't seen anything in the documentation that indicates that a sales order or invoice can be generated from a case.  I also don't see any systems that manage the authorization of a return for service.