I know a lot of people sell their cards through Paypal, which seems awesome. However, my only experience with Paypal is through eBay and I've learned that it's extremely easy for the buyer to pay, receive something, then file a claim and get the money back. If we sell cards via Paypal, are we simply working off of trust?

In my experience this is how Paypal works: If cards are purchased using Paypal gift, the seller isn't protected. If the cards are purchased under the "goods or services" option then the seller should be protected, but they will have to pay the Paypal fees.

Do you know how ebay items are paid through paypal? Is it gift or goods and services?

Ebay items are sold through and paid for via the goods & services option. When selling cards under $100, tracking and delivery confirmation is enough to prove delivery of a card you sell. When selling cards over $100, signature confirmation may be required as proof of delivery to the recipient. There are some general buying/selling via paypal guides you can google which apply to selling mtg cards online. Keep in mind when selling through deckbox you are responsible for proving your cards were delivered, aka people can scam you all they want if you don't track your packages.

Cool, thanks for the info.