There's a scene in Fallout: New Vegas that I find really interesting in how it uses skill checks in dialogue. A merchant company, the Crimson Caravan, want to buy out one of their rivals, Cassidy Caravans, and they hire the player character to negotiate the deal. The player has likely already met the rival company's owner, Rose of Sharon Cassidy, by this point - in fact, it's entirely possible that she suggested they ask the Crimson Caravan for work in the first place.
Cass is propping up the bar at a truck stop on the border near the game's opening area. She's heard that her caravan has been destroyed in her absence - her employees killed and their wagons burned in an attack on the road - but she can't investigate because of a bureaucratic hold-up. The man in charge of the border post, Ranger Jackson, has halted all commercial traffic across the border because of dangers on the roads - wild animals, bandits, and enemy soldiers - that the authorities are struggling to get under control.
When the player brings the Crimson Caravan's offer to Cass, she refuses on principle. Her business may have effectively been destroyed, but she's too proud and too stubborn to sell her surname for any number of messes of pottage. Convincing her requires that the player employs one of either their Speech or Barter skills - there are two options for each, requiring either moderate or high investments of skill points. Skill and Barter are the game's two Charisma-based skills, and it's not uncommon for them to appear side-by-side like this, but here, they diverge in application.
The easier Speech option is simple - the player just reminds Cass that, if she sells the business, she won't be commercial traffic anymore, so she'll be able to get across the border. She's itching to get on the road again, so this convinces her. (She will ask the player to help Jackson clear the roads for the benefit of her fellow merchants, but this is a very simple quest that they likely already completed hours ago.)
The more challenging Speech check is to tell Cass that there's no way her business can survive, so it's her duty to do the merciful thing - shoot it in the head, bury it, and move on with her life. This, naturally, brings her close to socking the player in the jaw, but she sees the truth in it. She's been holding onto the forlorn hope that there might be something left to save, but she really has lost everything. This bypasses Jackson's quest - she just wants to walk out and not look back.
The Barter options approach things differently - from the Speech options, and from each other. The more challenging one involves making some sport of the offer, challenging Cass to a drinking contest. The player has to supply the booze, and they run the risk of getting embarrassingly drunk if their Endurance stat is too low, but, either way, this will impress Cass enough that she'll sign the contract.
The easier Barter option, though, is, I think, the most interesting. It requires the player to sweeten the deal with their own money - a not insubstantial amount of it, in fact. Cass is still hesitant, though, which allows the player to make a very interesting point. With the money from the Crimson Caravan plus the player's contribution, she'd have enough to restart her business - buy new animals and equipment, hire a new crew, start trading again.
Further, the player can point out that the Crimson Caravan are unlikely to continue using the 'Cassidy Caravans' name after buying it. They're only buying her out to try to monopolise local trade, after all. If they don't use the name, they'll forfeit their rights to it - meaning that Cass can, as she puts it, take their money, give them nothing, and go back to running her business as if the attack never happened.
Cass, naturally, accepts this offer, though she's staggered that the player is so willing to sell out their employers to help her like this. (The player needn't feel any moral misgivings about doing so. A little investigation reveals that the attack on Cass's business was actually engineered by the Crimson Caravan themselves, in collusion with a crime family, in a conspiracy to wipe out their competition.)
I think this entire interaction represents how well New Vegas uses skill checks. Barter, in RPGs, is often a very barebones skill. Its use is letting the player earn more and spend less - as part of an equation determining shop prices, or in dialogue options that boil down to asking for money. It's not uncommon for Speech to be the skill of the peaceful, benevolent diplomat, while Barter is for common mercenaries.
Here, though, the Barter options actually cost more than their Speech equivalents. The player ends up out of pocket for a sizable chunk of change or at least a lot of booze. Instead, the Barter skill represents the character's understanding of common business practices and relevant laws. It allows them to convince Cass to accept a deal by finding a loophole that benefits her more than if she refused.
The equivalent Speech options, meanwhile, are effectively free, but do involve making Cass feel that little bit worse. They emphasise what she's lost, how trapped she is by her circumstances, and convince her to give up and let the Crimson Caravan win. In the long run, this doesn't make a real difference - once she leaves the outpost, she and the player can discover the conspiracy and get their revenge either way - but I think the choice does let the player say something about their character.
Part of the brilliance of this game is how little details, like Cass being stuck at the outpost, tie into other details all across the story. Caravan traffic is halted, in part, because deathclaws have nested near the roads to the north. They've nested there because the local quarry has ceased operations - the noise caused by the digging and blasting had previously scared them off.
The quarry closed down because escaped convicts raided it and stole the workers' stash of mining explosives. The convicts escaped because the government was using them for forced labour on the railroads, and foolishly entrusted them with enough dynamite to stage an uprising, seize control of the prison, and turn it into a fortress and a base of operations for banditry.
Similarly, the threads of Cass's story spread outwards, ultimately affecting the entire future of New California. When she learns that the Crimson Caravan and their allies killed her friends, Cass is furious. She wants to march over there and beat the snot out of the people responsible. The player can convince her to instead settle things legally - get proof of their crimes, pass them on to Ranger Jackson, and hope the justice system gets revenge for her.
If Cass does things her way, the criminals pay with their lives, but their bosses end up better off for it. With their regional execs murdered, the trading companies can claim that the government isn't doing enough to protect them - so, they don't have to support the government's interests, either. They withdraw trade, demand special treatment, and end up making their shortfall everyone's problem.
If the legal option is pursued, though, the evidence becomes blackmail material. The government has the trading companies over a barrel, and that lets them pass stricter trade laws. Given the choice of accepting regulation or facing criminal investigation, the crooked execs choose to stay out of jail. Those responsible for the murders technically avoid justice, but their hopes of a monopoly are dashed - and their superiors are unlikely to be pleased with them having hurt long-term profits so badly.
Cass's story is political and economical all the way through. It's about the influence of wealth on government, and the fundamental injustices of the carceral system. It's about revenge, and reform, and how to hit people where it hurts - their bottom line. And it's about how, sometimes, skills in an RPG aren't about making numbers go up - they're about how a character understands the world around them, and how they can apply that understanding to help someone out of a jam, or help reshape the trade lines of a whole nation.
