Okay, here's my research on card shuffling... it probably needs a rewrite
Once a reading is set up, the next task is shuffling the cards. Although it will not affect the outcome, Tarot cards have their own type of shuffle. Sources rarely recommend poker style shuffling for a variety of spiritual reasons. Most books recommend a method of hand-to-hand shuffling. Spiritual reasons not withstanding, this manner of handling cards, like other Tarot practices, has a practical function, which serves to make the deck last longer. This method not only effectively mixes cards but also reduces wear because this style of shuffling does not bend or flex the cards, like the poker shuffle. To achieve a Tarot shuffle, hold a deck in one hand and with the other hand take a card from the top and another from the bottom in series, until the whole deck transfers into the other hand. By using the thumb to push a card from the top so that it protrudes slightly and then placing it into the other hand, the whole deck easily transfers in quick succession. Often more than a single card will slide forth, which only serves to better mix the cards. What matters most is placing cards on first the top and then the bottom of the new stack in the other hand. After all the cards are mixed, the reader should set three stacks in front of the seeker and allow the client to restack the cards back into a single pack for the reading.
Dealing cards straight from the top is acceptable but by picking up each card, while keeping it face down and allowing the seeker to choose his or her cards, a reader provides better opportunity for real interaction. Allowing a seeker to feel they are taking part in forming their future is an imperative, if sorting through the issues in the present is a goal. Another style of card selection, which provides strong client participation, includes fanning out the entire deck face down and then asking the client to choose cards from anywhere in that deck. Instruct the client not to look at any card and instead hand you (the reader) cards as they are drawn. As the seeker passes each card, the reader can position it in the spread face up or face down; however, by concealing cards until all are drawn and then turning them up, card pictures and names will not cause the seeker anxiety, resulting from a prior card selection. Concern over the previous cards chosen might influence the cards selected later. When dealing cards directly from the top of a deck, extensive shuffling to insure that cards are properly mixed is required.
According to a newspaper article that appeared in the New York Times on January 9, 1990, two statistical researchers found it takes seven ordinary, imperfect shuffles to mix fifty-two regular playing cards thoroughly. Fewer are not enough and more do not significantly improve the mix. According to Dr. Persi Diaconis, a statistician at Harvard University, who co-authored the discovery, “There are people who go to casinos and make money on this.” Although a representative of the state gaming control board in Las Vegas reported that cards get shuffled from four to seven times, at the discretion of each casino, Dr. Diaconis said he almost never sees dealers shuffle seven times. He and his co-researcher Dr. Dave Bayer, a mathematician and computer scientist at Columbia University, watched numerous players shuffle to determine how well dealers interlace a deck during an average shuffle. To inhibit card counting, which describes a method of tilting odds against the dealer; most casinos use several decks simultaneously during gambling. Findings on shuffling multiple decks easily translate to Tarot. A Tarot deck requires nine or ten shuffles to be completely random from the last reading. An accepted school of thought among Tarot readers, however, suggests in a reading everything occurs for a reason. Consensus regarding shuffling shows that a reader will feel when the time to present cards arrives. Keep in mind over-shuffling causes unnecessary wear on the cards, especially if readers flex cards back into the stack.