Politoed just runs standard bulky water moves, tyranitar well... stuff tyranitars do you should know that and uhh hippowdon's shit, ignore it, and ninetales just dies basically and uses what you'd expect it to. Sometimes people sash them which can be problematic but in all honesty if they're using ninetales you've probably won already.
So basically when you see a weather starter it's probably going to do exactly what you expect it to but it depends on who's using it. I could go into intricacies at worlds level with the likes of tyranitar (protect mindgames with ttar are intense) but that's irrelevant for now since as a general rule everyone plays terribly at regionals. Do not overpredict, ever, because it's why so many people lose. One of the worst aspects of this game is that if you think your opponent's better than they actually are, you're setting yourself up for a massive fall. Not gonna fall for that one again, let me tell you.
So basically when you see a weather starter it's probably going to do exactly what you expect it to but it depends on who's using it. I could go into intricacies at worlds level with the likes of tyranitar (protect mindgames with ttar are intense) but that's irrelevant for now since as a general rule everyone plays terribly at regionals. Do not overpredict, ever, because it's why so many people lose. One of the worst aspects of this game is that if you think your opponent's better than they actually are, you're setting yourself up for a massive fall. Not gonna fall for that one again, let me tell you.