How exactly is he misrepresenting what he is selling? I believe this person was fully disclosing that he was selling the keys against the TOS of MSFT and that there is the risk that the keys may not work in the future.

IMO calling everyone that sells MSFT MSDN keys a scammer is only going to make is easier for scammers to scam because they all have negative trust, so it will be more difficult to differentiate from the ones who are currently acting honestly from the ones who are outright scamming their buyers (eg receiving BTC and in return give nothing, ever). This has resulted in many people scamming while pretending to sell MSDN keys, even after they have negative trust.