Depends on whether the previous owner consumed the ‘upgrade’ or not. Best way to figure that out is to add it to your current system, and check the website, or call Sonos Support directly to discuss it.

Does it work? Have you added it to your system? Or if it’s a Play:5 (gen1) added to S1?

If you are able to add it to a system, it should appear under your Sonos account online. You will then be able to see if the upgrade credit has already been used on it or if it’s still available.