Posting a few different thoughts from a long reading of this thread.
The question really is should insight be better than the 2nd level spell ZoT? That is subject more to DM interpretation. Also the DC is set by the DM, so a DC 30 for a stranger aligns with the general rule for Insight.
I'm curious, does anyone take Insight as a skill in your games?
I've got a friend who I play with, sometimes he GM's and he also does not allow Insight checks to decide if strangers are lying to us. He says it is unrealistic because we don't know these people well enough to know that.
I never take Insight when he is GMing, because it becomes a useless skill. We are traveling mercenaries who are rarely in the same town twice, let alone spending multiple weeks or months getting to know people in said towns. When the merchant says a bad crop means prices went up, is he gouging the newcomers to town or is this a plot hook? Sure, I can find out by asking around town, after I lose the extra 20 gold they charged us. This guy says he knows a secret way into the castle, is this a trap where 45 of the Dark Lord's guards are going to ambush us or the DM giving us a way in so we can continue the adventure?
Yes, in real-life I'd have to use my best judgement, but the game gives us an ability to see through deception. IT's why when we try to lie to the guards, we need to roll to see if they believe us. Otherwise, how could this guard know that the signet I'm showing him doesn't belong to Archduke Archibald and I'm his agent traveling in disguise with a message for the Lady. I'm lying through my teeth, we stole this ring five sessions ago from the guy's manor, but I need to roll so the guard doesn't know I'm lying. By the same token, I should have the ability to know whether or not these shady folk saying they've come to help us are lying or not.
Yes, I'd have to say you broadly misunderstand the playstyle. Firstly, I wouldn't adjudicate that statement at all. It's not the player's position to suggest mechanics, but the DM's. It's the player's prerogative to declare actions, and "make an Insight check" is not an action. I prefer clear goal and approach, so I can fairly adjudicate the action. I'll touch on this more in a moment.
A) there's a lack of an action declaration involving a goal and approach. I have a goal, but how are they doing this? Insight is a mechanic, not an action. This can be as simple as "I observe them for signs of lying" to more complicated, or even well off the insight path such as, "I yell at him I think he's lying and he better start telling me the truth!" prompted an Intimidate check.
B) there's a lack of fictional positioning to the example to allow me to successfully adjudicate what's at stake. Is the person the player's are questioning going to help the players? If so, then a failed check may result in them becoming angry at being questioned and withdrawing their assistance. ("I see you don't believe me. Fine, I shall take my business elsewhere.") Perhaps the players are risking loss of face because this is a prominent personage and they're in public? ("<GASP> [PC NAME] just insulted the Baron's son by suggesting he's lying!"} Or, maybe, this person is a run of the mill merchant and nothing is at stake, in which case, sure, I just narrate a success so we can move to more interesting scenes (and I make a note to not frame scenes lacking importance). But, there's none of this in the example, so I can't say.
For 90% of skills, I have no problem with this approach. If you are trying to lie to get into the palace, I need to know some form of the lie you are trying to sell so I know how the guard responds.
But, for insight... is there any other path than "I look for body language clues that they are lying."?
I mean, if I'm going to declare someone is lying to me... I'm going to declare that, not use that declaration to figure out if they are lying. If I'm going to ask more questions to see if their story holds up and or if they contradict themselves, that's what I'm going to do. If I'm asking for insight, I want to know what my character's gut and observation skills are gleaning off of this individual.
In this one skill, I really don't see how I could ask a player to give me more information, asking for the Insight tells me exactly what action they are taking because it is a sum of observations, not a multi-choice approach. At least, as long as I don't have super senses that can smell or hear a lie, like some super heroes I've heard of.
i.e. They are searching an empty room (I have nothing planned), the player is eager to roll, I let them roll. They succeed, they find nothing, should they fail I inject a complication - As they examine the impeccably smooth wall slabs, a myriad incorporeal hands reach out from the wall in an attempt to touch the investigating PCs, the veil of illusion drops as the wall reveals itself to be a writhing mass of incorporeal undead all seemingly bounded uncomfortably together in haphazard fashion....
One thing I want to add to this, sometimes when my players ask to roll for something and I didn't have something planned, if they roll really well I'll give them something extra.
Just recently a player wanted to loot a room in a castle, it was the room for the maids so I wasn't planning on there being anything in there, but it made sense there could be something, and they rolled really high, so they found a box with keepsakes from the prince. Or sometimes, they find a nifty item like a magic wine bottle that pours out the type of wine you request.
Failure probably would have netted them nothing (I do horrible enough things to them on purpose without me adding more, but I also sometimes add more because an idea strikes me mid-way through) but I like rewarding good rolls too, since nothing sucks more than rolling really high when it absolutely doesn't matter.
