Long story short: Cheating someone is too difficult in D&D.
Now a bit longer version:
Why I don't like it:
So if you're pretending to be someone you're not, you're going to get caught with a fairly good chance no matter what magic or clever ploy you use.
Why I don't like it:
In D&D it's hard to tell your wife that you had one beer even though you had two. Not to mention that if you tell the baron you killed all the orcs, even though you left one alive, you gonna be in a mess (Sense Motive is class skill of Aristocrats).
So I don't like the fact that social interaction (lying and noticing the truth), is a little bit too mechanic. I'd like my players to find out if someone telling the truth and not be sure about it until they have a proof. But Sense Motive works a little bit too much like a lie detector: Once you get +19 bonus to Sense Motive (you can easily get this at 7th-level, at least) you will always get the right "hunch" about everybody in 1 minute. It's pretty drastic, since it's not an opposed roll (opponent can't do anything about it). So effectively 7th-level Expert will know you're untrustworthy in 1 minute; whether you are or you're not. This beats even Undetectable Alignment.
But to defend Sense Motive, I must say that I once had a DM that utilized this skill in his games with style... He used the phrase "you sense that he's lying" as a plot-element, and it worked great. So I do admit - wholeheartedly - that Sense Motive and generally everything you find in D&D can be used to make the game fun and enjoyable. Sense Motive is like that also. I just feel that it's not my "thing" as a DM.
TBH I do cheat a lot with Sense Motive when I DM. I do it a lot. I want my players to find out if someone is lying, lie detectors are useless unless magic is used. Which also brings out the fact that Sense Motive requires very, very little innovativity from the player's part. If you cast a spell and know someone is lying, it's fine. You took the risk and effort to cast the spell. But a hidden roll "Ok, you got the right hunch" is not my cup of tea.
Now a bit longer version:
Hunch This use of the skill involves making a gut assessment of the social situation. You can get the feeling from another’s behavior that something is wrong, such as when you’re talking to an impostor. Alternatively, you can get the feeling that someone is trustworthy
Why I don't like it:
So if you're pretending to be someone you're not, you're going to get caught with a fairly good chance no matter what magic or clever ploy you use.
A Bluff check is opposed by the target’s Sense Motive check.
The bluff is believable and doesn’t affect the target much. +0 modifier to Bluff
Why I don't like it:
In D&D it's hard to tell your wife that you had one beer even though you had two. Not to mention that if you tell the baron you killed all the orcs, even though you left one alive, you gonna be in a mess (Sense Motive is class skill of Aristocrats).
So I don't like the fact that social interaction (lying and noticing the truth), is a little bit too mechanic. I'd like my players to find out if someone telling the truth and not be sure about it until they have a proof. But Sense Motive works a little bit too much like a lie detector: Once you get +19 bonus to Sense Motive (you can easily get this at 7th-level, at least) you will always get the right "hunch" about everybody in 1 minute. It's pretty drastic, since it's not an opposed roll (opponent can't do anything about it). So effectively 7th-level Expert will know you're untrustworthy in 1 minute; whether you are or you're not. This beats even Undetectable Alignment.
But to defend Sense Motive, I must say that I once had a DM that utilized this skill in his games with style... He used the phrase "you sense that he's lying" as a plot-element, and it worked great. So I do admit - wholeheartedly - that Sense Motive and generally everything you find in D&D can be used to make the game fun and enjoyable. Sense Motive is like that also. I just feel that it's not my "thing" as a DM.
TBH I do cheat a lot with Sense Motive when I DM. I do it a lot. I want my players to find out if someone is lying, lie detectors are useless unless magic is used. Which also brings out the fact that Sense Motive requires very, very little innovativity from the player's part. If you cast a spell and know someone is lying, it's fine. You took the risk and effort to cast the spell. But a hidden roll "Ok, you got the right hunch" is not my cup of tea.