As for other goblin leaders ... they both see themselves on top of foodchain ... you either proove them right, or wrong ... depend of your own character motivations ... Anyway they have no reason to bargain with you ... you either obey, or kill them ... anything else would be out of role.
As for intelligence ... feel free to think im wrong, but taken what things is tied to intelligence rolls, that stat should be more like named knowlege.
So what if they consider themselves superior, if this is not backed by any serious firepower? They are still just a bunch of goblins with overreaching ambitions. I was playing a githyanki, they also consider themselves superior. (They even get a line bragging about how they build their cities on corpses of gods.) The goblins have no reason to bargain with my character? Well, neither has my character any reason to bargain with them, because they have nothing to offer. And yet Minthara & co act as if they do; I guess they rolled a one on that intelligence roll.