Is the Pottermore quiz accurate?
For some people, the quiz is accurate over the long run: I have a friend who’s as Slytherpuff as they come, but on any given quiz, she’s not likely to draw a Hatstall – but over time, she’ll get about 50/50 Slytherin and Hufflepuff results (…well, even then, she has about a 3-5% of Ravenclaw, but it’s pretty accurate.)