If you buy a used Nest Cam, the previous owner could have access to it. The Wirecutter discovered a way a previous owner can view the images, via the Wink hub. It is unclear if the issue applies to other products. Oh, and there is currently no way to fix it.
If you buy and set up a used Nest indoor camera that has been paired with a Wink hub, the previous owner may have unfettered access to images from that camera. And we currently don’t know of any cure for this problem. We are unsure what further implications there may be regarding Nest’s video service, including whether it may be vulnerable to other methods or through other smart-home device integrations.