You should have factory reset it before selling it. Now, the new owner will need to do so, which will erase your account data from it, but it won’t disappear from your purchases on your account at www.sonos.com until such time as the new owner attaches it to their own account (part of the set up process after that factory reset). 

Thanks @Airgetlam .

Ok and if I didn’t factory reset before selling it. Something happens? I have to do it in my wi fi? Or he can do it and we can proceed?

He can do it, and proceed. It will erase your data from the device, and return it to ‘fresh out of the box’ so he can set it up. Once he adds it to his system, it will disappear from your purchased devices on your account at www.sonos.com. It should already have disappeared from your system when you open your controller, since it is no longer connected to your WiFi.