This is one of the reasons the used market for Apple devices is absolutely fraught with danger. If an Apple ID is left active on the device, only Apple can reset it. In most cases, they will only do that if they are provided the original purchase receipt for the serial number associated with the device. So in theory, removing the activation lock from owned devices is possible in a situation where a locked apple ID cannot be recovered if you are the original owner. IMO, there should be a process to release devices that haven't been used for a certain amount of time AND haven't been reported stolen. But there's very little incentive for Apple to do this.