Sense Motive vs. changing your mind

[Zaq]

Here's a situation I don't think the rules cover, and I'd like your opinions on what the most elegant way to handle it is.

So, let's say that you ask someone a straightforward question. For instance, "will you help me with XYZ?" Or something like that. And they answer you, not trying to Bluff or anything, and they say, "sure." You can roll Sense Motive at this point, even though they're not Bluffing, and for the purposes of this exercise, let's assume that your Sense Motive is high enough to beat their Bluff check outright, if they were Bluffing.

So you go on about your merry way, and it comes time for them to help you with XYZ. But at some point between when you asked for their help and when you arrived at where XYZ is going to go down, they changed their mind. They no longer want to help you with XYZ. They're tired and they want to go home, or they found out that XYZ is scarier than they thought it was, or something. So when it comes down to it, they're no longer willing to help you with XYZ, even though they said they were.

First off, should you be entitled some form of Sense Motive or other check to notice this ahead of time? Remember, we've established that your Sense Motive is good enough that this person basically can't lie to you. And they're not exactly lying, but they're definitely going back on their word. And if they outright state that "hey man, I know I said I'd help you with XYZ, but I changed my mind. I'm out," then that's not a Bluff, because they mean it. But let's say they've changed their mind and just haven't told you yet. Should you be allowed a Sense Motive or something to determine that they're not going to follow through on their word?

Second, how do you handle this is a way that doesn't render mechanics useless? Remember, they initially said "yes," and your Sense Motive determines that they weren't lying. Now, someone who was trying to game the system could claim that they initially weren't lying, but after they "truthfully" agreed to your suggestion, they independently changed their mind. That basically renders your Sense Motive check meaningless, and it lets them effectively lie without using Bluff. (At this point, we'd like to imagine that an involved GM would call BS on that sort of thing, but the fact remains that it's possible.) But by the same token, it's a little weird for a Sense Motive check to make things totally deterministic—real people do change their minds about things, and the fact that Sense Motive indicates that you weren't lying when you originally agreed to something doesn't mean that it's impossible for you to change your mind.

Like I said, I don't think the rules cover this very well at all, but I'd like some opinions as to how you'd handle this sort of thing.

[Troacctid]

Sounds like the standard DC 20 check to get a hunch. I'd use their passive score (take 10) and if they hit the DC, they get a sense that the NPC is getting grumpy or whatever.

[Killer Angel]

Sense motive is not "I magically foresee your future behavior".
A change of mind is perfectly reasonable and cannot be guessed by SM. But of course, the change must be based on something real, that happened and modified the conditions in which you are acting.
Because if someone changes mind every time he wakes up, then SM should tell that the guy is not reliable.

[Flickerdart]

I would allow Sense Motive to communicate not only "is thus guy lying" but also the degree of commitment to the statement. It's not actually that hard to determine if someone is saying "yeah whatever" or actually committing to it. This won't help you if the guy, say, gets his foot hacked off on the way to help you and has to bow out, but it lets you apply additional carrots or sticks to make sure the guy keeps his word.

[Elder_Basilisk]

I like the DC 20 hunch suggestion.

That could take the form of, "this guy leaves you with the impression he's a bit of a flake," "it doesn't sound like he thinks there's any danger involved," or "he's drunk; he may feel differently about the risk/reward ratio when he sobers up."

[Ashtagon]

Seems quite reasonable that Sense Motive is useful not only for detecting if someone is telling the truth (as they see it), but also whether or not they are motivated for the task. That is, you're sensing their motivation.

I wouldn't let it just mysteriously detect whether or not the person stopped work while you aren't in the area though. It's based on body language, not psychic powers.

https://www.youtube.com/watch?v=bcYppAs6ZdI