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I cant recall there being fake replicas of Ledger Nanos S (I do recall a 2018 article on Fake Trezor Ones):
https://blog.trezor.io/psa-non-genuine-trezor-devices-979b64e359a7). That does not mean it cant happen, especially if the market on a bull run, and that is why it is essential, as you say, to purchase the devices on the official sellers site (they will list official resellers if need be).
What we have seen are sites that allegedly sell Ledgers in bulk for a very low price (youll probably receive nothing at all there) and people that sell a preconfigured Ledger (as is described in the 34K$ case).
What made me think Ledger Nano replicas exist is when i saw them on eBay for 20 usd each and they had lots of sales. It was also New in Box. I just checked and they are no longer selling them that cheap, it was few months ago when I saw them. Or they could have bought original ones and did the custom scratch card with their own personal seed like this and sold them cheap to attract buyers:

Either way we should all be careful. I personally own a Ledger Blue myself and that's where i keep my crypto but i got it directly on Ledger website.

I think a cheap new ledger nano S is indeed very likely to be a preconfigured one. Some scammers are ready to invest real money, if the potential gain is huge. You can generate a new seed and it will probably be safe to use, but why take the risk ? The ledger is quite cheap bought from the manufacturer... On the same line of thinking, I can see no good reason to sell it used either.