Cards suit live selling better than almost anything, because the four things that decide value are invisible in a normal photograph and obvious under a moving camera.
What decides the price
Centring — how evenly the image sits inside the border. Often the single biggest factor on an otherwise clean card.
Corners — sharpness, under magnification.
Edges — chipping, especially on dark-bordered cards.
Surface — scratches, print lines, and gloss.
Then: set, edition, parallel, and whether it is graded.
Raw versus graded
Graded cards are sealed in a holder with a number from a grading company — the common scales run 1 to 10. The holder settles the condition argument and the market prices accordingly.
Raw cards are everything else, and this is where live selling earns its place: you can tilt the card under the light, show the corners, and let the room judge.
What to show
Hold it still. Tilt it slowly under a single light source so the surface shows. Show all four corners, then the back — back centring is frequently worse than front and frequently omitted.
Describing honestly
Use the trade's language and be specific about what you see. If you are not a grader, say so: "I would call this lightly played, but I am not a grader" is a respectable sentence and protects you.
Pacing
Cards sell fast. A show can move a lot of them, but auctioning twenty similar commons one at a time will drain the room — bundle those as lots and auction the ones worth a conversation.
Delivery
Sleeve, toploader, taped so it cannot slide, then a rigid envelope. Packing cards.
More: how to sell on Metzee, pricing cards.