The default is "we don't know".
Unless one or the other of the claims is widely improbable, then the default is "we don't know", and any claim otherwise, in *either* direction needs evidence.
In other cases where *both* options are widely improbable, then the default is also "we just don't know".
Spat lives on planet Mars. Spat was launched into space by NASA two years ago.
The default is?