It does have a population of 23 and $17,500 is the NGC listed price.
Trouble with auctions are if you get two people with deep pockets wanting the same coin, then this will drive the price up
as they bid against each other.
By the same token if only one person is interested, he can put up a lowball price and if no challenges him, then he gets a bargain. It sometimes is a crapshoot with auctions. It is the same with eBay, depends on how many are interested.
The only thing you can do is put up a high starting price but then this will drive away some bidders.
To answer the second part of your question, here again we will need more information.