If the timings are correct and the right astrological concepts are used then the predictions, will be accurate. This is true and a given thing for the most accurate and best Astrologer.
BUT, if the predictions are NOT appreciated or Guru Dakshina NOT given, then predictions will NOT happen.
Why?
Guru graha is the one which predicts (proposes) by a good Astrologer,
Shani being more karmic and powerful than Guru can dispose it, by your own karma.
And that KARMA is decided by you, to Appreciate or Guru Dakshina being given.
So be it, Tathaastu.
Addendum : Destiny or Fate can be modified, nullified, suffered or enjoyed by doing Karma (Action with an Intention, good or bad).