When you should avoid using a new tarot deck?
The first important thing is how much use tarot cards. How much you use cards matters.
Always purchase a deck for professional purposes.
First, read your cards what messages you are getting from the cards? Are you able to interpret yes or no? See what kind of vibrations you get from your new deck.
After that, you can read for clients. If the deck is old it is good to use and if you have new deck people feel you are a newcomer.