Fair market price is typically defined as the price agreeable to a willing
buyer and seller. If the seller just wants to get rid of an item, and all
the buyers are intermediaries who will be selling the item to some third
party, then the sales prices is kind of meaningless, or what I will call
wholesale vs retail.
Thinly traded items have prices that depend more on just who happens to
notice them, and how the first bid is arranged.
To me personally the fair price is my don't care price, ie when I offer
enough that I really don't care if the sellers answer is yes or no, thats
my top bid.