Sense Motive Rules?

[Sheogoroth]

Let's say I have a character with an abysmal Charisma(Like 1).
That character is trying to be nonthreatening and another character is trying to tell how nonthreatening it is.

Low-charisma rolls a 5 an gets a grand total of 1 for diplomacy, High charisma guy gets a total of 22.
The low charisma creature is a hideous mutant and with his low charisma could easily seem threatening, and one can assume that he would have difficulty expressing himself.
What on earth happens here?
Is this an opposing check?

[Curmudgeon]

Your question asks about Sense Motive, but then you introduce Diplomacy. These are different skills which have no interaction. Sense Motive is used to counter a Bluff, but that's not part of the scenario.

The target's Sense Motive skill or Charisma ability have no bearing on someone else assessing them. If another character wants to determine if the low-Charisma character is threatening (get a Hunch, DC 20), it's almost entirely up to that other character's Sense Motive check to make the assessment. The DM could adjust the DC of the Sense Motive check by situation modifiers (typically +/- 2); the low-Charisma character attempting transparency in their non-threatening status could result in such an adjustment to the Hunch DC.

[JungleChicken]

I would say in the use the a minus 1 for each 5 under the goal the hideous character makes and a +1 for each 5 over the goal the high charisma guy makes. Whatever the total be it positive or negative should be used to weigh the NPCs reaction

[cakellene]

I thought it was a fairly common standard that social skills don't affect PCs.

[Curmudgeon]

I thought it was a fairly common standard that social skills don't affect PCs.
There's a limitation to NPCs for Diplomacy, but not other skills. Any PC can be Bluffed, fooled by Disguise or Forgery, and have their secretive ways discerned by Sense Motive.

[Duke of Urrel]

According to the RAW: "Trying to gain information with Sense Motive generally takes at least 1 minute."

I don't apply this rule when a Sense Motive check simply opposes the Bluff check of a liar, but I do apply it when a character may get a hunch about someone or may sense that someone is enchanted.

What this means is that if I respond in a hasty and prejudicial way because of your hideous appearance, for example by running away from you, I may never get that hunch that informs me that you're actually a decent fellow.

On the other hand, if you use Diplomacy skill and I am not too repulsed by your looks to listen to what you have to say for at least a minute, then my Sense Motive skill should kick in.

But Curmudgeon is right; getting the hunch that you are trustworthy with my Sense Motive skill and letting myself be influenced by your Diplomacy skill are two different things. And Diplomacy doesn't work on PCs, but other Charisma-based skills do.

[Sheogoroth]

My DM tends to start our characters not knowing one-another.
I also prefer to play my character as my character would act with the given back story, with some obvious reservations of sanity.

Some of our players tend to roll lop-lopsidedly optimized characters, so it's an issue we have run into more times than i would care to admit
But that makes sense, so thank you all.