Swarmkeeper
Hero
As far as "punishing" players for asking for a check ... I don't. In the case of insight and a few other skills I use the better of passive or the roll.
Perhaps I was unclear. At our table, players declare an action and goal. If they jump ahead and start rolling, I gently ask them to describe what their character is doing and what they are trying to accomplish. No one is being "punished". Players learn to drop the habits of other games and adapt to the 5e mechanics. When I do ask for a roll as DM for an ability check, I also relay the stakes involved (i.e. the DC and the "meaningful consequence of failure"). The player can usually then decide if their PC would proceed with the potentially risky action or rethink things.
Having a PC in the party who is naive and gullible is quite common in my experience. If a PC's flaw is to be gullible and they're they only one questioning an NPC, the NPC can lie their ass off.
Agreed, if that is how a DM decides to play that particular NPC based on their bonds/flaws/etc. Then again, perhaps that NPC is overconfident and goes way over the top in his lie, even twirling his mustache as he's lying through his teeth, rejoicing in his ability to pull one over on these naive adventurers who think they are so special - and not realizing suspicious Brog is about to break him in half. I'm sure we can think of other ways to play it out, too.
As a DM I need some indication and reminder that they aren't going to be suspicious.
Absolutely. Having players role play their action and goal is a great way to get this out.
Player (Susan): Suiza trustingly asks the proprietor "We found a body in the alley out back, do you know anything about it?"
DM, now reminded that Suiza's character is the gullible type, might even grant inspiration to the PC. Suiza still might auto-fail (i.e. no roll called) since she's so gullible, but the player is reinforcing what her character is really like to everyone at the table.
So maybe a different question: a PC has the flaw "I put too much trust in those who wield power within my temple's hierarchy. " They're questioning someone superior in the hierarchy that is lying but is proficient at deception.
To me this is a scenario where I would like to call for an insight check, but I don't know my player's characters to that level of detail.
I agree - no DM should be expected to know any player's character completely. Over time, through role play, the DM will gain familiarity with the personality of each PC, but the DM has more than enough on his/her plate to keep the details perfectly straight. It is therefore up to the player from time to time to remind the DM (and everyone at the table) through first or third person role play what their PC is like - traits, ideals, binds, flaws, etc.
Player: With a deep bow of respect to my temple superior, my PC asks her...
For me it's simpler and more fair to the player's vision of their PC to let them ask for an insight check now and then.
To me, the table learns nothing about the character - or really what they specifically want to do and why - when the player just asks to make an Insight check. To be honest, I just don't find that to be an interesting style of play. Works just fine for some, but not for others.