Activation Lock

The original owner has to unlock the iPad. If the previous owner doesn't remember their Apple ID, then you can only try to get your money back. If not, a useless iPad has many practical uses such as a unique serving tray. If they "forgot" their Apple ID, there is also a chance that it is a stolen device.

https://discussions.apple.com/docs/DOC-250001038

Yes. But then you would just run into Activation Lock. Activation Lock stays until it is disabled by the original owner. They can also remove it from their devices list on iCloud.com as well.