Total noob question about selling stuff

[dako]

I dont get how to sell stuff to other players.

Like, I mean, if they have a shop open saying they will buy SBL for 5c right?
I click on their mushroom thing and it opens up a window saying to right click on items from my bags to sell the items right? So, I hover my cursor over the item I want to sell to the guy, and it says like SBL, 3c, the amount a vendors give me. So, I right click the item and it only gives me 3c, instead of the 5c the guy was offering!

Im just wondering what I'm doing wrong, if theres something else your supposed to do when selling stuff to people.

Thank you for the help!