Well if it said Nanite it did say Nanite. It’s still not a good practice to have a ridiculous amount of verts if not required. Those models are difficult to modify and clean up manually and it does matter for performance.
In case it’s a scan, which naturally produces tons of verts, specifically made for Nanite, then that’s also a different situation than someone who modelled a football manually in Blender ;p.
I once refunded a model on another marketplace because it was impossible to clean up. They had made a scan of a creature and did no attempt to clean it up before posting it on their marketplace. It didn’t have a million verts like you’d see on some scientific mummy scan but it was complex enough that it couldn’t be cleaned up manually to prepare it for rigging. Nanite did not exist at the time ;). Given a context like that you can decide if it’s a product flaw or not.
You can luckily request a refund within 14 days and I believe the request is granted even faster if the seller does not reply within time.