To add to that comment:
Almost none - you could even say none at all. Having worked in the industry, I know that no company wants to do that because it’s too expensive, especially in a globalised world. As I mentioned in a previous comment, there are shipping costs to consider, as well as the cost of refurbishing the device. The worst part from a business perspective is having to offer at least a one-year warranty on a used device.
Simply sending it back to the warehouse is often not enough; it has to be sent to the company headquarters instead. A special department has to be set up there, complete with staff, tools, replacement parts, a system for re-entering the serial number and proper repackaging. It’s just not worth the trouble.
After all, safety is a major concern here! Just imagine if the device caught fire or the customer got an electric shock. If you are refurbishing, you must follow the entire safety protocol required, for example, by EU regulations or US.
At the companies where I worked, we simply gave customers $100 as a gesture of goodwill, regardless of what they returned. Old devices were then disassembled and used for repairs, in consultation with the customer - for example, to keep the price down by using replacement parts from the old device instead of new ones. Customers could indicate whether they wanted new or used replacement parts.
For those looking to receive more than $100, however, we would always recommend using existing dealers who specialise in refurbishing devices. This industry already exists and operates exceptionally well.
In fact, there are companies that offer something similar, but that’s a whole other topic. They have contracts where you don’t buy the hardware, you just rent it. In exchange, you always get the latest model and don’t have to worry if it malfunctions; you will receive new hardware the very next day. As I said, though, that’s a different topic. It’s an option for customers who always want the latest device, though. This option is also available for 3D printers, but, as I mentioned, the contracts are expensive and not worth it for hobbyists.
Ultimately, it all comes down to money. The company certainly isn’t going to cover the costs if the customer decides to switch to something else after several months. The loss in value would be too great. We all know how customers treat their devices.
I don’t even want to describe the state of some of the devices that customers have brought in for repair or return - it’s often shocking. A device that smells of urine is actually the least of my concerns. Even worse are customers who have tried to tinker with the device themselves or send it back completely disassembled.