Is that Cenoceras or Nautilus?

[Cicija]

To pester the forum members again with two questions. 

1. Is it a Cenoceras? This nautiloid is up for auction, it comes from Madagascar, it is 12 cm * 9 cm * 7 cm in size.
The seller lists it as Nautilus and estimates its age at 120 million years (Lower Cretaceous). Looks like Cenoceras to me? As far as I know, Cenoceras has a range of fossils from the Upper Triassic to the Middle Jurassic (from 235.0 to 163.5 Ma).
 
2. The seller states that it has been manipulated. I see it's polished. Is it authentic enough for a fossil collection or is it more of a decorative item?

[Ludwigia]

It looks like a polished Cymatoceras, which is a Nautilus genus from the Madagascan Early Cretaceous which can regularly be found online.