I would answer your questions in 2 sections.

(A)Is the direct respons

and

(B) is a case study and you could draw your inference from it.

(A)The direct response

Though astrologers may differ in their predictions in terms of preciseness (and I am talking about astrologers NOT quacks) but their general direction of prediction would be on the same lines. Sometime people have told me that astrologer/s did not tell them about the bad stuff or sugar coated their predictions.

Now coming to the part about guarantees !

I am reminded about two ancient saying/s which hold a lot of relevance even today. 

“There is no guarantee about anything in this world except death”. I firmly believe that we do not even have any guarantee from God, that we would be taking the next breath. So every breath we take should be taken as a blessing from God and we should all focus on doing good karma and self improvement. That is easier said than done. Most of us fail as it requires 

 The 20 spiritual guidelines are a very good starting point for doing good karma and gradually making it a part of one’s life or habit. I am providing the link below. There are the essence of all the Hindu scriptures.

My Gurudev used to say that “लोभ, भय, मोह, माया, क्रोध, अहंकार,हिंसा or Greed, fear, temptation, delusion, anger, ego, violence are personal traits which would surely makes ones life fall into a ditch.