I personally am totally against that mentality some people have that retailers are always obliged to accept returns and that it's fine for the customer not to pay anything. It's exactly how you are thinking - "You have to pay 20% plus shipping just to demo them" - yeah, you have coz Noble is not running some kinda of international audio gear demo program - they are into the business of selling units and if you are a reviewer with enough experience then you might receive a demo unit.
IMO once you've used a product it's not a brand new product anymore - it's a used one ... period. Just because a lot of retailers allow it that doesn't mean that they don't lose money over it. For instance, if you go to a store to buy new headphones the open-box items will always have a lower price and I expect it to be at least 15%, and while the customer who returned that product doesn't realize it, the seller is losing money because of that - first because he had to lower the price, second because an employee of his is getting paid to put that item back into storage, to go through the inventory and list it and stuff like that.
So you might be thinking - "I should be paying only the return shipping and that's fair." but then who is paying the employee who packed your package and shipped it, who is covering the price of the shipping of the product to you, who is paying to the employee who retrieves the returned package, cleans it, gets new tips for it, handles the paperwork and returns it to the storage etc.
Now, whether a 20% fee is justified is another matter but it's definitely not like the mentality "I just pay the return shipping and we're even"