There was another thread on here a month or so ago about someone that bought an Apple Watch used and couldn't get it to pair with their iPhone because it was still paired to someone else's AppleID. The discussion entailed going to your iCloud account to see if it was listed there after pairing. I bought my AW used, so was happy to see that mine was. Then today, while trying to make some changes to my AppleID (not iCloud) with 2 factor authentication, I was trying to access support. When you try to connect with support, the webpage asks you to pick your device to get support. All of the ones listed were older devices I no longer used, so I proceeded to add all the serial numbers of my current devices. When I got to the Apple Watch, it said it was registered to another AppleID. So it was showing tied to my AppleID in iCloud, but in my Apple support profile for my AppleID, it still said it was someone else's. This concerned me because it has AppleCare+, among other concerns. I had to call Apple about a problem with my security questions so while talking to them I mentioned the problem with my AW and they were able to correct it so it shows registered to me now. Thankfully they took my word for it, and could likely see it was paired in iCloud. I had already established my identity for the security issue, so I guess she trusted me. I was very worried she'd say I needed to contact the prior owner to have them do something to de-register it. That would have been impossible since I bought it from a reputable store on eBay many months ago. So if you have bought an AW used, you may want to check and see if its registered to someone else still, along with the iCloud check to be able to pair it. I was logged in and on this url - https://supportprofile.apple.com This may not be an issue at all, but something to be aware of if you are buying used. There is an option on the page I listed to remove a device from your support profile.