I often see folks say that you really have to handle your deck before you buy it, especially if it's your first deck.
Here's what I think. If people can meet their spouses online, you can buy a deck of tarot cards online.
If you have access to a store, or a place where you can see the whole deck before you buy it, that can be a lot of fun! Truth is, I live in a rural area and don't have access to those kind of options, so buying a deck online was more practical for me. You can also do a lot of research on decks before ordering them, with some websites showcasing hundreds of decks.
I only have a couple general suggestions for people planning to use cards for reading (i.e. as opposed to getting them solely as a work of art). In order for those suggestions to make sense, though, it helps to know how a typical tarot deck is organized.
The Major Arcana, or trump cards, are numbered zero through twenty one. They represent a progression through stages of life, or typical events and people that most of us encounter. Their meanings are derived from a unique character or item portrayed, like the Star, the Hermit, Death, the Tower, or the Lovers. They take on special prominence in spreads, and in the original game-playing use of tarot, they outranked number cards (think of the expression, "The issue is trumped by extenuating circumstances.")
The Minor Arcana are made up of four suits: cups, pentacles, wands, and swords. These are numbered similarly to traditional playing cards, ace through ten and then the court cards. As in playing cards, the king ranks highest, with the queen second highest (though I idiosyncratically read queens as higher). Next in line is the knight, or in some cases, the prince. Finally, the page, or sometimes princess, is the lowest ranking court card.
Now, the Major Arcana are almost always illustrated, and court cards often have at least something pictorial. But the numbered Minor Arcana sometimes only have pips, or the corresponding number of symbols. In fact, the original tarot decks probably had pips instead of pictures for the Minor Arcana. This means that they look more like traditional playing cards.
So what does this mean for you? Well, it means that a deck listed as having "illustrated Minor Arcana" will have unique pictures on each card that will help you associate it with a distinct meaning. If, instead, the Minor Arcana are listed as illustrated with pips, it means that there will just be the suit symbols. These can still be beautiful decks, but they are much harder if you are just learning. Many readers who use pip cards incorporate numerology in order to read these cards; that is an intriguing approach, for sure, but I like to keep it relatively simple.
This leads me to my first suggestion: Get illustrated Minor Arcana! The very first deck I bought only had pips, and trying to memorize meanings was frustrating and arbitrary. When I got my Rider-Waite deck, I was suddenly able to connect the card meanings to what I was seeing. Learning tarot became much more rewarding.
A few other suggestions are simple: check online reviews if you can, seeing if anybody says anything about the paper quality and sturdiness. When you get your cards, check for the Little White Book (LWB) that comes with almost every deck; this usually entails a card-by-card explanation and a few suggested spreads. The quality of LWBs varies greatly, with some being useful and creative, and others confusing and poorly written. Ultimately, I was able to come up with a better sense of card meanings by checking out books from the public library.
Keep these things in mind as you are buying and receiving your deck, but ultimately, don't overthink it. It's always great to find that deck that sets your heart on fire, but you can also spend a lot of time searching for the Perfect Deck without ever getting your hands on some actual cards. Get illustrated Minor Arcana, check your local library for tarot books, and have fun!