Well, Crimea is home to mostly ethnic Russians, but Westerners conducted numerous (in-person) independent polls and found the same results. I also looked at the OSCE reports, and after Crimea annexed, violent attacks ceased, yet continued in separatist regions.
Maybe all of the surveys are inaccurate, but maybe they're not. I don't know, but I keep in mind the US, the EU, and Russia have their agendas. We'd be foolish to believe we're not misled.
This survey included the Tartars and Ukrainians:
https://www.opendemocracy.net/en/odr/crimean-conundrum/
The OSCE has been in Ukraine and surrounding regions monitoring the civil war for over a decade: