I don't know much about this, but your best best is to find a local community group dedicated to the specific type of collectible and then see what shopping service is most commonly used - esp if you are worried about breaking during mailing. Compare your pieces with what's listed, as far as quality, price, and demand. Then tailor your sale to fit how quickly you want them gone. Def make sure to look up mailing cost and include!
If using ebay or craigslist, make sure to take many good photos!