As a person who sells on here quite often, I do try to research the things I list; however, I also try to go by what I paid for the item. I do not recoup my original cost, that is not the intention. I think that most of us selling on here are trying to either clean up our sewing rooms, or are passing along a good bargain we found in the clearance section.
And, yes, I check prices online before buying-passed up something last night that was much more expensive than other places online.