For me this song is about the concept of writing and stretching the truth. In the lyrics, we here about the writer and the tattoed girl discussing their dedication to be readers and writers of fiction. This is prompted by her tattoo. If the writer is telling the truth about this, then they are not writing fiction. The answer to 'why would I lie to you?' is because the song is about a love of fiction. Why would I lie to you?
For me this song is about the concept of writing and stretching the truth. In the lyrics, we here about the writer and the tattoed girl discussing their dedication to be readers and writers of fiction. This is prompted by her tattoo. If the writer is telling the truth about this, then they are not writing fiction. The answer to 'why would I lie to you?' is because the song is about a love of fiction. Why would I lie to you?