The commonest pricing mistake in this category is treating age as value.
Age is not rarity
A coin from 1820 that was struck in millions is common. A coin from 1980 struck in thousands is not. What matters is how many exist in this condition, which is a question about the series rather than the century.
Know the series you are selling, or say that you do not and let the room price it.
The floor
Precious metal has a melt value, and that is a real floor below which you should not sell. Put it in as a reserve rather than as a high starting price.
For non-precious coins there is usually no floor, and a low start works as it does everywhere.
What the room pays extra for
A clearly shown edge. It separates a seller who knows from one who does not.
An honest attribution, including uncertainty.
An original surface, explicitly stated as uncleaned.
Lots
Bulk and circulated common dates sell better as lots than individually. Describe a lot by count, period and what is guaranteed, and do not imply that anything unexamined might be rare — that is how a lot becomes a dispute.
Questions people ask
Should I get coins graded?
For high value, it settles the argument and widens the audience. For common material the fee exceeds the gain.
What if I do not know what I have?
Say so and sell it as unattributed. Collectors will often tell you in the chat, and that is worth more than a guess.
Can I price from a catalogue?
As a reference. Catalogue values and auction results are different numbers.
More: selling coins.