Please read this if buying a second hand Apple Watch.

[Col.bris]

Warning to buyers of second hand Apple watches.

Be aware if you purchase a second hand Apple Watch the seller MUST sign in to iCloud and remove the watch from his or hers list of Apple products owned. Just wiping the watch does nothing for the buyer. I suggest you request proof that it is all good. If not you cannot Pair the watch. Period. The following is the official Apple instructions
Colin
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Turn off Activation Lock before you send your Apple Watch in for service, sell it, or give it away

Before you send your Apple Watch in for service, sell it, or give it away, you should turn off Activation Lock on your Apple Watch. Just unpair your Apple Watch from your iPhone:
Keep your Apple Watch and iPhone close together.
Open the Apple Watch app on your iPhone and tap the My Watch tab.
Tap your watch name at the top of the screen, then tap .
Tap Unpair Apple Watch. For Apple Watch Series 3 (GPS + Cellular), tap Remove [Carrier] Plan. If you aren't going to pair with a different Apple Watch or iPhone, you might need to contact your carrier to cancel your cellular subscription.*
Enter your Apple ID password. If you forgot your Apple ID password, you can reset it.
Tap again to confirm.
If you can't access your iPhone or Apple Watch, or if your Apple Watch isn't paired with your iPhone and you need to turn off Activation Lock:
On a computer, go to iCloud.com and sign in with your Apple ID.
Go to Find My iPhone.
Select All Devices, then click your Apple Watch.
Click Erase Apple Watch. Select Next until the device is erased.
Click X next to your Apple Watch.

 

[scifan57]

The difference here is that you can’t tell if Activation Lock is turned on until you try to pair the Watch.
The only satisfactory way for the seller to prove that Activation Lock has been turned off is if he does it right in front of you. This is a product that can be very risky to buy sight unseen.

 

[cowy]

nice info thanks!