What? Are we still talking about 気持ち悪い? It means creepy/disgusting and that's exactly how it's being used. ZUN's not saying Yukari's a liar, he's saying she's creepy, which as I said is entirely a visceral emotional reaction. It says nothing about the person being described other than how someone else is feeling about them.
Edit: Wait, you mean 胡散臭さ? I believe that's referring to the part in the latest Strange Creators magazine where Reimu describes Yukari as "suspiciousness itself, wearing a dress and walking around." Which is just to say that she's really suspicious and shady, from Reimu's point of view. It's definitely a fun description, but there's nothing that requires a deeper analysis about it.