Ask early, and ideally on the listing before the show — where the answer stays for everyone who comes later.
The questions
"What is the exact issue — year, mint mark, variety?" Rarity lives there, not in the century. "Old silver coin" is not something you can price. Non-answer: "It's very old."
"Has it been cleaned?" The most important question in the category. Cleaning is permanent and immediately visible to anyone who knows the series. An honest "yes, before I owned it" is fine; a vague answer is not. Common mistakes.
"Can you tilt it under a light?" Hairlines and cleaning marks appear at an angle and vanish straight on.
"How are you grading it, and do you grade?" A band and an admission beats a confident number from somebody who does not grade.
For notes: "How many folds, and can I see it flat in even light?" Paper money is graded largely on folds and crispness.
For anything in a holder
"Is the holder PVC-free, and how long has it been in there?" Soft PVC flips degrade and leave a green film on the coin. It is a real and common problem.
What protection covers
A different issue than described, undisclosed cleaning, damage not shown: seven days from delivery.
Questions people ask
Is toning the same as damage?
No. Natural toning is normal and often desirable; corrosion is not. Ask which you are looking at.
Should I ask for a weight?
For anything where weight is part of the standard, yes.
What if the seller cannot identify it?
That is an honest answer. Bid as though it is unidentified.
More: buying coins, what they are worth.