Kelley blue book prices?

2 questions. First, on kelley blue book, it says that the "suggested retail" price for a toyota prius is $23,000 and the "CPO" price is 23,450 - why is the CPO price more? Second, do these prices represent what the sticker price should be? if so, how much lower should i expect to negotiate? one of my friends said the rule of thumb is that you should be able to go $2,000 lower than the sticker price - is this right?