Ask before the lot comes up. Public questions on a listing are read by everybody who arrives later, which is why good sellers answer them properly.
The questions
"Can you show the back?" Centring and staining appear there first, and a seller who only shows fronts may not know that. Non-answer: another front shot.
"Can you tilt it under the light?" Scratches and print lines exist only at an angle. This is the request that separates a seen card from a photographed one.
"Which printing is it?" First edition, unlimited, regional, promo. They look alike and are not alike.
"What do you think is wrong with it?" The best question in the category. "Soft bottom-left corner, centring off to the right" is somebody who has looked. "It's mint" about a raw card is somebody who has not.
For graded cards: "Which service, and can I read the label?" Numbers are not interchangeable between services. And check the slab for cracks.
About predicted grades
Nobody can promise what a raw card will grade. If a seller gives a number, treat it as an opinion and bid on the card in front of you. What cards are worth.
What protection covers
Damage not described, a different card than shown, a slab described as intact that is not: seven days from delivery. A card that grades lower than somebody guessed is not, unless they stated it as fact.
Questions people ask
Should I ask for it out of the sleeve?
For anything valuable, yes. Sleeve glare hides exactly what you are looking for.
Can I ask for it measured?
Yes, for a valuable raw card. A trimmed card measures short.
Is it rude to ask several things?
No. A seller who minds is telling you something.
More: buying cards, how they are graded.