Coetzee leaves a lot of breadcrumbs throughout part 1 to undermine Barton's (Mrs. Cruso's) lack of credibility as a truthful narrator.  Barton asks Cruso why he doesn't keep a journal of his time on the island.  She states, "with every day that passes, our memories grow less certain" (17).   The narrative in part 1 is not a journal, but rather are letters written in retrospect to Mr. Foe.  If memories grow less certain as time passes, then how can we be certain that Barton's memories are truthful?  She then lists off the memories that she believes were important to write down: "the prayers of your companions, your terror...your gratitude...your fear...the discomforts" (17).  These are not feelings that Cruso told Barton, they are projections of what Barton believes Cruso felt, revealing her bias and predisposition to believe that Cruso responds to stimulus (i.e, savage beasts, sleeping in a tree, etc...) in the same way that she would.  When Cruso dies, Barton changes her name to Mrs. Cruso in order to make her path easier.  She acknowledges that she did this, yet thinks very little of it: "what kind of woman was I, in truth? - but took his advice and so was known as Mrs Cruso to all on board" (42).  She did this earlier too when she told herself the foma, "I am safe, I am on an island, all will be well" (14).  Who is to say whether or not she would bend the truth in order to make the path easier in other circumstances?