I hate Sense Motive and similar skills. The ability to detect lies is not a given even for the people who do it for a living. Investigators, journalists, lawyers etc are frequently had over by liars in their day to day business.
If you're a PC in my game then I expect you to make your own judgement about whether an NPC is giving you the run around. If you make an effort to find out then you'll have more to go on. If you just want to roll your d20, well you're going to miss out and quite frankly you deserve to because it's lazy gaming in my opinion.
So, get out and about. Find out where this NPC hangs around, ask questions, buy drinks, threaten people, look stuff up, put the word out, check out what they tell you or reference it with someone else who might also know. Yes, this takes time. It might not be as much fun as smacking the heads off random goblins but how far are you prepared to trust these people. I mean, I just made them up. They're hardly going to be on the straight and narrow, surely?
Are you ever going to get a concrete answer? No. You cast Know Alignment and nothing happens because it's a stupid spell that has no effective meaning in any way other than a meta game concept of behavioural codes that does not exist outside of the DMG.
Play the game well and you will be rewarded, rely too much on the rules and you will be reviled. Don't believe me? Sense my Motive...