its obvious that from the sellers point of view the best price is the highest price he can get., whereas from the buyer's vantage point the best price is the lowest price enabling him/her to purchase the component.
so, if a buyer asks the question "what's your best price", tell him that it is the listed price, because that is the price the seller would like to receive.
if the buyer wants to buy the component, he will probably offer a lower price.
some ads do not include "obo" . this doesn't mean, a seller won't accept less than his stated price.
a little humor sometimes helps.