It is not bad to use someone else's tarot cards at all. In fact, if you visit a good psychic tarot reader in person, you will most often be asked to shuffle the cards at the start of your reading. A busy psychic will have had their cards used by thousands of people. If you want to read your own cards, it is possible to buy used cards on eBay. I've always sold my old decks that way. Some people prefer their tarot decks to have been pre-loved by a good psychic.