The book opens with a translator's note, not by Arthur Golden, but by a fictional translator who isn't actually a character. Like a geisha attempting to fool a client, the book masquerades as a non-fiction memoir written by a real geisha. But also like a geisha, whose makeup is so thick it's clearly makeup, we all know the book is fiction. Arthur Golden's name is on the cover.
However, it's easy to immerse yourself in the book through Sayuri's first-person account. Also, it being a "memoir," she often attempts to portray herself in the most positive light possible. That's also another geisha trait—manipulating things so that she always looks good.
In a first-person book like this, there is always the danger of having an unreliable narrator. Sayuri may be deceptive, but we don't think she is a liar. Plus, we see in one scene that she keeps a diary, so her facts as she presents them are likely accurate.