Many characters lie. There are a number of reasons to do so such as outrunning a dark past, deceiving in order to protect oneself, or trying to get one over on another, just to name a few. Lying in character is acceptable, with two exceptions. If a character lies while under an effect that compels them to tell the truth (such as an Obey, Sense, or Command effect) when this effect can’t be or hasn’t been resisted through allowable means (such as through skills or through the SP cost of a spiritual effect resist), then that is considered cheating. If a character lies in game in order to metagame (subverting character knowledge for OOG knowledge either to receive IG benefit or to avoid IG consequences), then that is also considered cheating. Please keep these stipulations in mind when your character lies.
Likewise, it isn’t uncommon for people to avoid telling the full truth to each other out of character/out of game too. After all, sometimes we want to preserve the secrecy of roleplay and character details. If someone asks you a question about a character and you do not wish to tell the truth, “find out in game” or “FOIG” is the best response. Another great response is just “it’s a secret” or “I can’t tell you that yet.” This way, our community can continue to be open and honest with each other, even when there is a mystery that someone is trying to preserve.
There are instances when lying out of character crosses into the realm of metagaming. Lying intentionally to try to alter character action is never acceptable. For example, if Molly Mayhem approached Carl Chaos and asks if his character is an assassin sent to kill her character, Carl's completely in the right to say “find out in game.” However, if Carl lies to Molly saying, “My character is definitely not, but if you give me that rare item you have in-character, I can grant you an in-game boon,” that's blatant metagaming and will be addressed as such.
Remember that the goal of Call of the Void is to tell engaging stories together. Those stories may sometimes rely on not telling each other the whole truth, but they do depend on mutual trust and respect. The goal is playing to have fun, not playing to win.