Interesting question.
I think that the claim can be said to be fraudulent, though perhaps not the deck itself. Surely if you buy a pack of cards marked as "Poker Cards" and you find a deck with a 11's, 12's & 13's in place of Jacks, Queen's & Kings, you would be a bit miffed that the claim was made? Sure- you can play poker with such a set of cards, but are they still poker cards? Some of my favorite poker games couldn't be played with such a deck (suicide kings & one-eyed jacks are wild). This is a bit of a radical example- but what if the Jacks Queens & Kings are all there, but they are radically different- perhaps not in the look (a casual glance at the cards may not reveal that all the Jacks have 2 eyes, or that no Kings have a sword through their head). A collector buying the deck and expecting an "English" deck of cards would feel defeated and defrauded if it was advertised as such. It might be in the same style, but the content of the cards is different than the norm.
In a TdM, if the hermit is suddenly holding a book rather than a lamp, does this not change the character of the card? Other seemingly subtle changes throughout the deck will change the character of the whole deck, no? So if you have such a deck for sale, and claim it to be a TdM, isn't it a false claim?
If a RWS deck was sold as a "Tarot of Marseilles", wouldn't this be false advertising?
I have the Tarot of Bologna, which I consider to be TdM, but some do not. The differences are pretty subtle, but for some people, they are enough to change the label this deck carries.
The interesting question is "where is the line drawn: what makes a TdM?". Is it a style, the content of the cards, or a combination of both?
If it is a style, then we are limited to woodcut decks (or decks that were made to look as if they were woodcut decks). Bold black lines surrounding a limited pallet of colored areas... Almost as a cartoon from a modern newspaper.
If it is content- well, this is where there are differing opinions. I don't have the time or knowledge to say much about this, so I'll leave it to someone else.
My feeling is that there is a little bit from each category. Clearly content is important. Scenic pips prettymuch disqualify a deck from being considered a TdM, in my opinion. Also, decks with one or more majors replaced with different cards (Juno & Jupiter, for example) get the axe. But can the hermit be wearing earmuffs rather than a hood? Interesting question that I'm not prepared to answer.
For my money, the Serio deck seems to qualify based on the scans above... Certainly it is outside the norm for TdM.
-tb