No Touch Deck -- or Do! Or Don't! Or Do!
The "Don't let other people touch your deck" rule is rooted in the concept of residual energy: the idea that others will leave some kind of psychic or energetic residue on the cards, and that this residue is powerful enough to influence the performance of the deck.
If having a personal deck that no one else gets to touch helps you think of a deck as special, dedicated, consecrated, or specially tuned to your energy, then, by all means, shield that deck from the hands of others.
That said, I have hundreds of decks in my personal collection, and I've always encouraged people to handle every single one of them. One way I keep decks in circulation is to offer clients four or five decks to choose from, and people love looking through the cards to find a deck they enjoy. Allowing other people to handle and shuffle my cards also keeps them from thinking I've "stacked the deck" to make certain cards appear.
I've worked with literally hundreds of readers over the last ten years or so, and almost all of them allow others to touch their decks, with no reports of contamination or "deck failure" as a result.
My personal take: my Tarot cards are seventy-eight pieces of laminated cardboard, printed on a commercial press with mass-market ink. The "magic" that goes on during my readings arises from the hearts and minds and spirits of those involved in the readings ... not from the cards themselves. So why not let people touch the cards?
Unless, of course, they've been eating peanut butter fudge. Sticky fingerprints are really annoying!