Haggle/Financial stats.

You have to dump way too many points to even make it of any worth. And the discount isn't that substantial either. It's not like GOG or Steam sales where you get a 75% discount off your purchases. Doesn't happen in fictional games, ironically.

Mercantile skills are often of questionable use.

It really comes down to whichever resource is more scarce: gold or skill points (if the game uses a skill point system).

For games with improve-by-use systems, there's the question of how long it takes to improve the skill versus how long it takes to get the money that would have been saved.

Another issue would be games where you improve your skills by spending money; do you spend the money early to boost your skill, or do you instead spend the money to help you get through the early game to later when money is easier to come by?

A similar issue comes in games that have skills that affect the rate of skill points, as seen in Star Ocean 2, modern Might and Magic, and Lords of Xulima has a skill that increases XP gain (leading to more level ups, hence more skill points; note that this is a game with finite encounters).

Vampire the Masquerade: Redemption had a stat called Manipulation.

Raise that high enough and you can sell stuff for more than the purchase price.

I don't think there would be a pawnshop that wasn't bankrupt if I had that skill.

It's also possible in Morrowind, though I'm not sure if 100 is enough.

Raise it high enough (for example, with Magic or using Fortify Luck potions), and merchants will accept arbitrary deals, so you could sell an alchemist a Racer Plume for 4000 gold if the merchant has that much.

Now we just need to locate an enemy that can drop Racer Plumes. Anyone know where in Morrowind I might find one?

Any language skill. do GM's ever bother most wouldn't even remember it and if you were really fastidious you would have to have like a bazillion formal & cockney varients for every sub culture of each race.
not wasting skills on that when a better use is a magical google translate spell.

I thought that Luck was a dump skill in Fallout, until I learned about the sniper perk: on a ranged hit, the chance for it to be a critical is luck*10. So playing with 7 luck means every shot that lands has 70% chance of being critical. Actually a bit OP

Definitely not in Gothic 2 with NotR installed. The language skills there allow you to read the tablets that grant skill boosts, and there are plenty of tablets.
In most cases yes, but for example in Lords of Xulima you'll sure want it.

There are other games where the Luck stat is useful, perhaps even overpowered. For example:
* In Wasteland, Luck affects the damage you do with weapons other than explosives, and is the only stat to have that effect with ranged weapons, High Luck + SMG/Assault Rifle can get you tons of damage, as the Luck bonus is applied *per hit*.
* In Averrnum 1-3, for each point of Luck you have a 5% chance of not dying when otherwise dealt lethal damage, to a maximum of 95%. So, 19 Luck gives you a 95% chance of surviving anything; it may be expensive, but it can be a quite powerful build to try, and the game makes it feasible to learn some Priest Spells afterwords. (Note that this does not apply to the more recent remakes. I believe it *does* apply to Exile 1-3, however.)
* In Morrowind/Oblivion, it influences may things; in Oblivion, almost every skill adds a percentage of Luck to skills when used. The stat can't be increased quickly through leveling, but fortifying it can be incredibly useful. (In Morrowind, custom Fortify Luck potions make you better at certain skills without bound (and Alchemy is one of those skills, allowing you to increase the attribute exponentially), and in Oblivion it's one of the best custom enchantments you can put on armor before you've maxed out the important skills (though, unlike in Morrowind, it can't increase the effective value of a skill past 100).)

Also, Luck is usually a stat, not a skill.

LOL awesome thank you so much for finding that Lifthy! Really appreciate it - still as good as the day I first saw it ;)

Yeah, that's a good pick. Even in games like Morrowind, Daggerfall, or Oblivion, it doesn't really seem to matter all that much. Mostly due to them being so buggy as to be a technological biohazard.

Last I checked, Morrowind and Oblivion don't have language skills. (Probably because they were useless in Daggerfall.)

Final Fantasy, however, uses language as a plot point; there's a town where everyone speaks a strange language, but in order to get a mandatory item, you have to be able to talk with them. Of course, there's a quest to learn the language; you need to get a slab (rosetta stone) from a dungeon and take it to a person in a town to decipher it.

Magic of Scheherezade also does this; there's a town in the past where everyone speaks a different language, and you need to hire a translator before you can understand them.

(Note that neither game has skills as we think of them; understanding the language just requires you to pass a certain test.)

Luck was brilliant in Exile which later became the avernum series if i remember correctly it handled such things as your assassination attempt success rate and could be spread around the party; which in the exile series was many more times the current avernum 4 character D&D trope.
It's a pity in the day i couldn't afford to upgrade the demo and nowadays spiderweb softwares stuff is a dumpster fire to all that was good.

Avadon and Avernum series, in order to invest in skills at the top of the skill tree, you have to invest equal or greater number points to prerequisite skills first. In Avadon, a range-oriented Shadowalker will want to take Razordisk Training, the problem is you have to put points into Steel Discipline and Blade Training Training first, both melee skills.

In Underrail, social skills are situational, making them questionable choices for your precious skill points. Evasion and dodge skills are generally considered all-or-nothing.

Classic Avernum isn't like that; it's only the later Avernum remakes that do that.