This is equal parts explanation of how dialogue skills work in my world, justification to myself regarding the events of the Great Asosan Recruitment Debacle of '003, and clarification on how Diplomacy works in general.
I hate dialogue skills. Why analyze your opponent and create a convincing argument or lie when you can make a skill check? It's lazy and leads to poor planning. Luckily, I have house ruled dialogue skills in my campaign. The way they work, as noted in all versions of my campaign book, is that your check result does not guarantee success or failure. A poorly thought out line of dialogue can negate a super high check and a well thought out line of dialogue can compensate for a low check. This means you have to actually say something to the NPC in addition to making a check and it does not solely depend on the die and your bonus to the check, and some people just plain won't believe your lie, agree with you, or do what you want. Because they're assholes.
I like this for a few reasons. Firstly, it renders any sort of super optimized min/maxing for talking your way past everything completely inert. Secondly, it forces a player to interact with my NPCs. Thirdly, it makes players think before they start talking instead of making a skill check and then start talking. Fourthly, it still allows a player who may not be the best at public speaking to utilize dialogue skills and allows a crafty orator to talk his way out of a bad roll of the dice.
The reason I bring this up is because during our last session Cary tried to recruit some Asosans to the cause of Fort Jagged Tooth. They were deserters that did not approve of the priesthood of the Armiger being all gung ho about putting Asosans in front of bullets, and they were unwilling to fight people with guns, against Asosa, or alongside Goebleen. I don't know if you are aware of this, but Fort Jagged Tooth is completely reliant upon the Goebleen. There are like thirty Goebleen hanging around the Fort pulling guard duty and patrol duty and lookout duty and all the Fort's food and supplies come from the Goebleen. I also don't know if you caught this, but the Goebleen are not exactly super tolerant of outsiders. They grudgingly work with the pirates, but don't trust them and are nearing the point where they sever relations with them. They also have a bit of a chip on their shoulder because no one helped them out when the Asosans sterilized a large portion of their women folk and stopped paying their tithes to the Underhel races so the demons and undead would wreak havoc among the Goebleen warrens in Asosa. They're not terribly trusting or inclined to be nice to outsiders, unless they have something they want. Something like guns and explosives, which they've pretty much figured out, so they no longer really need to deal with the pirates.
Anyway, Fort Jagged Tooth is primarily populated with Goebleen. The Asosan deserters said they won't work with Goebleen, because you know, several hundred years of mutual hatred and terrorist attacks and warfare and bitter stalemate status. Since Gob was with the group, the Asosans can clearly see that this group works with at least one Goebleen and seeing this, were reluctant to jump aboard the Fort Jagged Tooth bandwagon. Cary, as Donovan, ignored this (and the fact that Gob said he and his crew would peace the fuck out if a bunch of Asosans and giants got on the company payroll) and continued to make a skill check in Diplomacy. You cannot convince a Holocaust survivor to work alongside a former Nazi oven technician and to act as scouts in Jewish ghettos for you while they're at it, at least not for minimum wage and no health insurance. Words aren't magic. They're words.
This kind of house rule doesn't mean I need to know every single detail of every NPC's life. It just means I need to understand my world, and knowing that Asosans and Goebleen don't like each other is a pretty common/basic chunk of background info. It's along the same lines as pirates like liquor, sorcery is unreliable in The Known World, Fallen are good at magic, Sereth really like/are good with rifles, and Elduman are organized. The rule isn't meant to be a trick either, I've never pulled out nonsense like, "Oh, you didn't know it, but this NPC's daughter was raped and murdered by thugs asking him to lower his prices on supplies, so he attacks you for complimenting her beauty in the photo he has while asking him to lower his prices." That's just crazy. Unless the NPC is important, like Gob or Vanden, the automatic fails and noes are going to be broad strokes stuff. Stuff like Kussethians don't like Dwenoren and Rankethlek probably distrust sorcery and don't like Fallen. These aren't complex or secret details of my campaign setting, this is common info readily available to the players.
Ultimately, this isn't even a house rule, it's a rule of the game. If you read the Diplomacy skill description, there is a line that says, "Some requests automatically fail if the request goes against the creature’s values or its nature, subject to GM discretion." So it's not like I'm an innovator here introducing alien concepts into the game. I guess it's more along the lines of clarifying things. I dunno, I hate dialogue skills and would remove them from the game if I could justify it.