[Anaraxes]

Why do you say "can never lie"? I remember the bit in ITL about goblins never going back on their word. But that's not the same thing as not lying. "Your word" refers to deliberate sworn oaths, not everything that comes out of your mouth, and going back on your word would just be not contradicting yourself -- which in the lying case would just mean sticking to your lie, not telling the truth. (The literal oath-keeping trait is given to goblins on Cidri, but it's an obvious nod to the common occurrence of that trait in mythology, whether faeries or other supernatural creatures.)

Given that even faithful goblins are allowed to adhere to the letter of the oath rather than the spirit (again, hearkening back to those fey or demonic bargains), I think even a honest, truth-telling goblin would be allowed to deceive with the truth. Even humans have been known to observe that telling the partial truth is the best way to lie. Or as Mr. Spock would say, he didn't lie, he just exaggerated.

If you want really pure creatures that are so intrinsically honest and honorable that they wouldn't even consider any sort of lying, you probably don't want to use the word "goblin", unless you're intentionally trying to subvert tropes and go for the surprise value. More like "angel".

If you're looking for any sort of realism -- not necessarily a given in fantasy -- then oath-keeping is merely a cultural trait of goblins, an ideal and something that parents try to teach while raising children, not an intrinsic and unalterable property of brain structure. So any individual goblin might well be a despicable oath-breaker by the standards of that culture, even if most of them do have remarkable integrity. But then, you notice how many humans don't live up to their ideals of their cultures.