Unfortunately, he is not violating eBay policy, even if the ethics are totally wrong. My guess is his "official" eBay account IS selling to legitimate buyers at $95, perhaps with some friends and family helping him out using their eBay accounts.

He then has a secondary batch of books that he sells via his other account at $300. Either he or perhaps a contact in his office, home or local area, has access to that account and is likely using a different laptop, perhaps on a separate internet connection as well. That would only to be cover his ass and sidestep eBay's automated policy checking.

eBay does not like VPNs and seems to detect shared VPNs, which often sees bids or listings cancelled or accounts shut down - and very quickly.

That said, even if he was managing both accounts from the same IP, MA is not violating any selling policy on Ebay, where you are allowed more than one account when selling different items. And he is of course!

One account is selling the 2nd Edition, while his official eBay account is selling the 3rd Edition, and rarely is there much overlap.

That might be why he keeps publishing multiple editions of his book - nothing more than to game platforms like eBay and perhaps in some way, Amazon as well.

Here is the eBay policy:
https://www.ebay.com/help/policies/listing-policies/duplicate-listings-policy?id=4255