The obligation of the seller is to describe the item accurately, provide a picture of the actual item (not a stock photo), and to ship the item within the shipping and handling time the seller entered for the auction. The first part is where a lot of sellers make mistakes.
There is a lot of wiggle room and nuances for ungraded cards that you have to be careful about. For example, if you pull a card straight from a pack, you should not use a condition of ‘New’. The ‘new’ condition includes the word undamaged, which, for a Pokemon card, means no edge wear, no surface wear, no dings, no tiny minor scratches at all. Since even a pack fresh card can include edgewear, this gives the buyer wiggle room to submit a claim that the item is not as described. A ‘New’ condition also includes the word unopened, which, obviously, is not possible for a Pokemon card that has been taken out of the pack.
Another common mistake is using condition qualifiers like ‘Near Mint’, ‘Lightly Played’, etc. without having a definition included in your listing what those words mean or entail. By not providing your own definitions, you may sell a card with a tiny tiny crease but otherwise looks perfectly fine and the buyer still submits a not as described claim. Why? Because their definition of Lightly Played (as backed up by other sources on ebay) say that Lightly Played does not include any creases (this is just an example).
For graded cards, you should not include any description of the flaws or lack of flaws at all! Which means don’t use a condition of ‘New’ and don’t say in your listing that ‘this card looks PERFECT’ or ‘this card is FLAWLESS’. When you do these things, you’re giving an opportunity to the buyer for a not as described claim. It is better to underdescribe than to overdescribe your cards.
If you want to look at a pro’s listings, take a look at PWCC’s auctions. Every single card (even the BGS 10 Charizard) has a condition of ‘Used’ and there is no description about the card’s condition whatsoever. The description might include what set the card’s from, whether it’s first edition, the population of the grade for that card, the popularity of Pokemon and their increasing prices, that kind of thing, but not the condition of the card.