To my knowledge, if the ‘buyer’ won’t factory reset the speaker, you can’t ‘remove’ it from your account. You could call Sonos Support directly to discuss it, but I suspect they don’t have the ability to modify that data. 

You could transfer your system to a different email account.

Not sure that affects the showing of the device in the ‘account’ section on www.sonos.com. Just changes the email associated with that account and all associated devices. 

It should only change the associated devices that are online and connected to the OP’s Wi-Fi at the time, not the Roam that has been sold.

if it doesn’t work, they can always transfer system back to the current email.

Edit: I’ve used the Transfer System Ownership numerous times registering 2nd hand devices to my account; it doesn’t transfer every associated device belonging to the previous owner, only those connected to the app at the time of transfer.

Interesting. Counter to the way I thought that system and database worked, but personal experience always beats assumptions. ;)

For your reference, I previously bought job lots of Bridges when the 15% upgrade credit became available on them.

I factory reset each one and add to a brand new S1 system with only the Bridge. The previous owner is listed as account holder and I use the Transfer System Ownership to change the registered owner to myself. If the app transferred every associated device from the previous owner, I’d be checking my Sonos account for 30% upgrade credits lol, but it’s only the respective Bridge that appears.

Not a dig at the Author of this thread….However, one should always factory reset a Sonos product before selling it. Sonos is no different than a computer in that respect.  One wouldn’t sell a computer without erasing the drive and/or factory resetting it. 

Factory reset your Sonos product