Rather, it depends on what the retailer (the one selling you the product) pays for the deck or book!
My advice as a Tarot author and deck creator? Buy your decks or books at Amazon.com or some other place that gives you a discount (we can all use the break, right?). Please note, though, that if you buy a Tarot book or deck used or at the "remainder table" (it will have a black mark on the outside pages), then authors/artists do not get royalties on those sales.
Supporting a retailer, especially one that charges full price for decks (plus shipping and handling), does not mean more money for the author/artist in terms of royalties! In only means more money for the retailer.
So next time you're about to pay retail price for a Tarot book and deck, think long and hard why you're doing it...because a Tarot author or deck isn't benefiting from your paying full price.
-- Janet Boyer, Amazon Hall of Fame/Vine Reviewer, author of Back in Time Tarot,Tarot in Reverse (Schiffer 2012) and the Snowland Tarot (Schiffer 2013). Featured in Tales of the Revolution: True Stories of People Who Are Poking the Box and Making a Difference (A Domino Project eBook edited by Seth Godin)