I 95% believe in nibali for one very important reason alone. when as a junior and early u23 he went to north italy like anyone would to get pro. he was already a big talent and yet he choose for the small local team g.s. mastromarco. back in the 2000s and before, italian elite cycling was all about money, results and all sorts of doping. only in recent years have they got rid of many teams and structures that were full of doping.
however nibali could go to any of the big teams, that also pay alot, yet he choose for mastromarco team, a team with 100% clean reputation in a very dirty era. he was a pretty large talent with good results in u23, but not gigantic like some other riders (thomas dekker, brajkovic). yet when he became pro he became better and better.
take ulissi or ratto, monstrous junior talents already riding for a horrible team. doped to their eyeballs they came out of junior in pro immediately and ratto is gone for good, now he has to be clean and ulissi nowhere near what he used to be, at least has some talent. the mere opposite of nibali's trajectory. there are countless other examples as well from riders 1990 and older especially
another example to me is aru. he came from palazzago team, probably the team with the worst reputation in all of italy. they have reformed their ways but I don't trust aru one bit. last years giro was a 100% bloodbag imo. since cycling is now so clean the dopers can easily be traced, even if they are microdosing. but those few % make the difference. aru would've never won those final stages and finished on the podium without that.
there's a reason nibali dislikes aru and I'm sure it has to do with him not trusting aru either