In the Dragon Age GM Guide, on page 17 I find mention of:
For example, a merchant may try to convince an adventurer to spend more money than he should on a new shield. The merchant would make a Communication (Bargaining) test while the adventurer would make a Willpower (Self-Discipline) test.
It's also used to resist Daze (PG p51).
In the Rogue class section for Bluff, it mentions "You must first use a minor action to try to deceive him. This is an opposed test of your Communication (Deception) vs. your opponent’s Willpower (Self-Discipline)". This seems okay for me since it sounds like the Rogue combat bluff is more like pointing and exclaiming; "Holy moly, would you look at that!" and then stabbing them when they look. Self-Discipline from the target lets them resist from looking away like a chump.
From the looks of it, each of the Willpower focuses are variations on a theme; faith, courage and self-discipline would seem to me to be different means to an end such as seeing something through against adversity or trying to withstand something. I'm not sure about detecting lies or falsehoods, however.
I would agree that it depends on what the intentions are; if it was an emotional argument they are trying to make then probably Per(Empathy). Maybe they were trying to twist teachings of Andraste to support whatever they are trying to say, then that could be against Cun(Religious Lore). Com(Deception) could easily be used to just see if the person recognized a liar or not (the words might be fine, but the person 'acts' like a liar and tips off the target).
As for the game itself, sure there's no chart of specific examples, but there's plenty of examples given through the text. In the GM guide on page 17 again:
(...) There are only eight abilities, so picking the right one should be intuitive. Remember that abilities are quite broadly defined.
Picking a focus may require more thought. Sometimes it’s obvious. If a character is trying to sneak through an alley, that’s a Dexterity (Stealth) test. Other times, the right focus is not as clear and indeed it may be that no focus applies. In that case, it’s just a straight ability test.
You should try to be open to player suggestion, though.
If a player can give a credible explanation for why a particular focus should apply to the test, you should allow its use.
Note the bolded text too; since the text of Deception says it is for "(...) lying to and tricking those less mentally adept than you", you could just call for a straight-up Cunning test if nothing else really applies.