For your question is it bad luck to buy your own tarot deck simple answer is No. Cards do not bring bad luck to you but bad lucks is always around a human. You do not know next minute what bad is going to happen in your life. All predictions do not tell the full detail of your future only some events that may happen.

If you do not want to buy a tarot deck you can just make one by yourself. after you learn the symbolism. This is how I did I bought a blank deck of cards and symbolized them. Always remember the four suits ♠ ♡ ♣ ♦, four seasons, four elements, four classes of people 1-Nobility 2-Clergy, 3-Merchant class, and 4-working class. They are all co-related to each other.

Similarly, each card has its own words and explanations but these are only predictions. They are not 100% correct compare to other spiritual things like white magic.

Also, you must know the configurations and arrangements of the tarot cards according to their information. Each pattern of arrangements means something specifically different. Furthermore, each card also relates to others individually.

Moreover, this is all requires personal experience to help you develop your intellect. If you are reading by yourself understand your problems, work through the past to predict your future.

No, it is not bad luck! there are a few superstitions tacked onto tarot cards, which includes keeping them wrapped in silk (with the belief that silk is magical in itself and has protective traits) and that the burning of them is important when you have worn them out. Or that you must purify them with a light of the total moon each month. All-time you read or pay attention to such things as that, memorize the rules had been made by expert people wiser or more spiritual a being than you.

Tarot cards are always magical. I own over 4 different decks of tarot cards two of them are gifts and other I purchased by myself.  If I was waiting for someone else to give me tarot cards I would not have been reading cards.
For reading tarot cards you must feel connection to them. You can get your own cards and study them and learn so you can train yourself.

As an astrologer I use them on the situation where someone does not really know about time of birth or day of birth. That may not provide the info your client looking for. The idea is behind that ask question shuffle cards connect with your higher self. You need to practice on it.