A camera is better than a photograph and worse than your hands. Knowing which way each error runs is most of the skill.
What a screen hides
Surface wear. Fine scratches, hairlines and creases are invisible head-on and obvious at an angle. This is the big one.
Depth. A chip looks like a mark; a dent looks like a shadow.
Colour, reliably. Screens and lighting both lie, and whites especially.
Smell, which for old textiles, books and storage finds is a real part of the condition.
Weight, which for metal, glass and anything claimed to be solid is a genuine authenticity signal.
What a screen exaggerates
Gloss. Bright light makes worn things look newly polished.
Dust and lint, which look like damage and wipe off.
Any flaw the camera happens to be close to. A chip filmed at 10 cm looks catastrophic. Ask for it alongside the whole object.
The four requests that fix most of it
"Tilt it to the light." The single most useful. It reveals surface wear nothing else shows.
"Turn it over." The back is where the repairs, marks and labels are.
"Hold it next to something ordinary." A hand, a coin, a ruler. Scale on a screen is unreliable.
"What is the worst thing about it?" Faster than any inspection, and the answer tells you about the seller as much as the item.
How to ask a seller about an item, live
Ask for the number, not the adjective
Measurements, not sizes. A measured length is a fact; a size label is an opinion.
Weight, if it matters.
The mark, read out, not described — hallmarks and maker's marks are where confident guesses go wrong.
Category-specific
Flat things — cards, comics, prints. Corners and edges, at an angle. Grading letters mean different things in different categories, so get the flaw in words too. What do NM, VG and the rest mean?
Ceramics and glass. Ask them to run a finger round the rim and foot, and to hold it up to a light — a hairline crack shows through.
Textiles. Held up to light for thinning and holes; the hem and underarms for wear.
Anything with glue or foam — shoes especially. Ask them to flex the sole. Age kills adhesive whether or not anything was worn. What does deadstock mean?
What protects you when the camera cannot
The description is what a dispute is decided on. If the listing says no chips and there is a chip, the screen's limitations are not your problem. You have 7 days from delivery for anything damaged, faulty, wrong or not as described, whatever the store's policy says. What if the seller lied about the item?
So the useful move when you are unsure is to get the seller to say it in words. A spoken answer in a public chat is part of the description.
More: five questions worth asking before you bid, what is provenance, condition words.