It is trivial to fake an IP address...you dont even need to use a VPN. There are services that will allow you to have what appears to be a residential IP address of a distinct location.
You don't say

But based on the fact that most accounts offered by the shady person (a.k.a. account seller) only have english posts and this account additionally is active in the german sub, it is very well imaginable that the account got hacked.
We can't be absolutely sure. But if the IP log shows a login from a completely different IP / country while trying to sell this account, it is very probable that it got hacked.
Therefore i will change my neg trust rating to a neutral one if a trustworthy member of this forum confirms the IP log shown.