Old social media accounts are available for sale exactly because they look more legitimate. (I'm just pointing a general fact, not that the user in question is a shill.)
I read an article describing the fenomenon, I can't find it now but there's plenty of interesting results if you search Google.
I'd be surprised if people were selling HN accounts for this purpose, it's much easier to reach a larger audience, and have more impact, on a general social media site than HN. I wouldn't suspect the practice is likely to happen here.
I read an article describing the fenomenon, I can't find it now but there's plenty of interesting results if you search Google.