A lie using the Bluff skill can only make a creature believe a lie is actually the truth—the creature's response to that belief is beyond the liar's control
No matter how good your Bluff skill check result when telling a lie, you can't force the victim to react in a certain way. This means until the GM finally draws the line and says, for example, that it's actually completely and utterly impossible (not just impossible) to convince anyone you're a pickle, lies can convince victims of less than that. However, what it means to the victim after you've convinced him that a lie is the truth—that is, what the victim does about the lie—is up to the GM.
Examples are addressed in turn below.
Example: The Guard and Gust
GM: The guard's Perception skill check beats your Stealth skill check, but you have total concealment. The guard says, "Who's there?"
Player: I say, "It's just the wind."
GM: [Sighs.] Make a Bluff skill check.
Player: I got a result of 30.
GM: [Rolls dice.] "Huh," says the guard. "I better check on the wizard to make sure his new talking wind spell is working okay."
Then play continues from there, likely requiring more Bluff skill checks. Instead, though, the GM could've just drawn the line there, saying that absolutely no one in that GM's low-fantasy campaign would believe poppycock like a talking wind. Nonetheless, in a typical Pathfinder setting there's actually a whispering wind spell, so a new spell that a guard's never heard of that makes wind really talk? Not impossible. However, the PC can't control what the guard subsequently does about the talking wind—the guard may take out his sword in case the wind's hostile, look around for a physical manifestation of the wind in case the sinister wind's trying to steal what he's protecting, or attempt to interrogate the wind to see if it overheard him gossiping with his coworker about the guard captain.
Example: The Guard and the Grit
GM: As you creep through the darkness, the guard appears unaware of your approach.
Player: I drop some sand down the guard's pants.
GM: [Sighs.] That's the surprise round, and that'll take your standard action and a successful melee touch attack against the guard's flat-footed AC.
Player: My attack roll result is 18.
GM: That's a hit.
Player: "I've filled your pants with itching powder!" I say. "I am so zany!"
GM: [Sighs.] Make a Bluff skill check.
Player: My Bluff check result is 30.
GM: [Rolls dice.] The guard totally considers the ramification of having itching powder in his pants, but, since the sand doesn't actually itch, the guard says, "Looks like your alchemist buddy sold you a bad batch. I'm not itchy at all!" The guard appears ready to fight you.
In other words, in all likelihood, this just won't be that helpful.
Example: The Noble and the Nightshade
Player: "An excellent vintage, your highness," I say. "Does the nightshade that I added to the wine—to which, of course, I have built up an immunity—add a little punch?"
GM: [Sighs.] Make a Bluff skill check.
Player: My Bluff check result is 30.
GM: [Rolls dice.] The king looks horrified, takes a potion from his pocket, and chugs it. Then he says, "Guards, seize this miscreant and toss him in the dungeon for his attempted regicide!"
There are dozens of ways this could play out, but most will involve the victim assuming he succeeded on the first saving throw against the poison then doing something, like the king above drinking a potion of neutralize poison (or, in lesser kingdoms, antitoxin) or a less accommodating victim just straight-up trying to murder the PC before the victim himself thinks he's going to die anyway. Spinning an elaborate lie might convince a victim of some equally elaborate scheme involving the poison, but the liar won't ever be able to impose psychosomatically a poison's effects.
Example: The Guard and the Guard Captain
GM: You round the corner and run smack into a guard.
Player: "Thank heavens I found you!" I say. "I'm the captain of the guard. An evil wizard has infiltrated the castle and is using polymorph any object spells to make castle residents look like handsome devils like me!"
GM: [Sighs.] Make a Bluff skill check.
Player: My Bluff check result is 30.
GM: [Rolls dice.] The guard looks confused and torn. "That sucks, I guess," he says.
A lot of what happens next—if the above even happens at all, the GM possibly ruling that this is a flat-out, nuh-uh, no-way impossible lie—depends on too many factors to list. In a world of magic, that tale could, in fact, be plausible—if highly improbable—, and, if the guard believes you, he may allow you as the faux guard captain to order him around if you make a successful Diplomacy skill to make a request (which should be easy if the guard thinks you're his boss).
