If you're going to be a tarot reader, you're going to run into bad card decks. It happens. You'll find the perfect deck online, and find that one of the cards is ripped, or one of the cards is missing. Or you'll use the deck for a little while and the edges will start foxing - pulling apart at the edges. Or you'll get two of the same card.
There are a few things that you can do. If you're missing or have a damaged card, email the publisher. Most of them will happily send you a replacement card, and all of their information can be found on their websites.
If it's an independent publisher, it's a little more iffy. I've written to one person, Robin Ator, who published the Prairie Tarot - which is one of my favorites. My dog ate one of my cards and I was heartbroken. He emailed back right away and asked me to send a few bucks for postage and sent me the replacement card right away.
I had another indie deck that had a damaged card, and the publisher said that I needed to by an entirely new deck for the full price, because they didn't issue replacements. That sucked, but it's their call, so just know that going in.
If the cardstock is bad, you can reach out to the publisher to see if they've improved the cardstock since you've bought the deck. If they haven't, it would be silly to get a replacement. I usually just suck it up and use the deck until it's past redemption, and then I cry.