Checks and opposing checks (3.5)

[McMindflayer]

Right, so here is something I've been fuzzy on since I started Dming games. How do you determine when to tell your players to roll a check?

To clarify, What I mean is: if a NPC is lying to your characters, do you tell them to roll a sense motives check, or do you wait for them to ask to roll one?

Like if there is something you hid, do you tell them to search or just let them decide whether to search?

Essentially, do you ask them to make a check that would make the player recognize that something is up, whether he succeeds or not?

[Eldariel]

To clarify, What I mean is: if a NPC is lying to your characters, do you tell them to roll a sense motives check, or do you wait for them to ask to roll one?

Either let them do it passively or just always have them throw Sense Motive when there's social interaction with meaningful information involved.

Like if there is something you hid, do you tell them to search or just let them decide whether to search?

They should decide if and when they want to search an area, but generally PCs are expected to search e.g. a dungeon before leaving; most of the time already while entering 'cause that's the only real way to find traps.

Essentially, do you ask them to make a check that would make the player recognize that something is up, whether he succeeds or not?

Overall, it depends. Some checks, have them roll regardless of whether something is up or not. This includes Spot, Listen, Sense Motive and like. Alternatively, DM can roll passive checks behind the screen if you don't want them to derive (or expect that they can't keep that information purely OOC) that "something is going to happen" or "we are being lied to based on our poor roll", but if your players can keep IC and OOC-knowledge separate, it shouldn't be a problem anyways.

Others, well, active checks are always something PCs should decide to do for themselves. Search, active Spot/Listen, Disable Device, the like are checks that people roll because they decide to use said skill. In those cases, if they don't decide to throw, they obviously don't throw then (though in some cases, e.g. Elves get free Search when within 5' of secret door so some abilities can generate passive exceptions here).

[Curmudgeon]

The player may make a Sense Motive check for each Bluff check made against their character. This seems optional, so the default would be to do nothing unless the player speaks up. Alternatively you could use their "take 10" numbers for Sense Motive to represent passive skepticism. Since that requires no special player effort and yet can help to advance your storytelling I'd suggest giving it a try.