@aramis, fair enough, I haven’t really gone back and re-read that section in a while. That all said, I think att/dis are situational. You can’t blanket assign something, because characters of all background can lie (eddington was an excellent liar, but so was quark. They don’t really share a common discipline, just as an example). I guess you instead need to consider the content of a lie. Using a lie as an example.
Generally speaking I think this system is built more around being able to roleplay these situations, rather than turning to mechanics (a strength for some, and a weakness for others).
@MisterX, But do you want your players to just outright know that the npc is being truthful? If so, then you don’t need mechanics as you might as well just tell them that.
If, however, you want the option or illusion of option for the npc to lie, then having the rolls contested adds a layer of uncertainty for the players. Likewise, if you only ever have a roll when there is deception, then it becomes obvious that the character is lying.
But you are right about intentions aligning. A success from either without any complications should be seen as a success.