Use cases would include customers receiving a discount on their Sale Order if they send in a used product 

 1) Create new operation type - let's call it Used Product Return

2) Create a Used Product Return Route

3) Have a consumable version of the used product -- selecting the Used Product Return route on the Inventory configuration (can also select on SO line) 

4) Add the consumable on the SO line. This product  will show up on the delivery and the receipt (but it doesn't matter either way)

5) If they need to actually track the used product we use the receipt that was generated from the SO to add the actual storable used product with the serial # attached or any other details they need to capture on the product 

6) Bonus steps -- To make sure this isn't confusing to customers you can modify your Delivery Slip to not print lines for certain product names, codes or product categories. 

In the backend, the delivery will look like:

But your Delivery Slip will print only the products the customer needs to see: