Turnitin AI detection, a legitimate tool or just educated guessing?

I've been thinking about this a lot lately, especially after a few people in my program got flagged for work, they genuinely wrote themselves. Turnitin keeps getting marketed as the gold standard for AI detection in academic settings, but the more I look into it the less convinced I am.

The way I understand it, Turnitin doesn't actually know whether something was written by AI. It measures how predictable your sentence structures and word choices are statistically. So, if you write clearly, use consistent grammar, and structure your arguments well congratulations, you write like a robot apparently.

What really bothers me is that institutions are treating these percentages like hard evidence. A professor sees 74% AI and suddenly you're in a misconduct meeting defending work you spent weeks on. There's no appeals process that actually accounts for writing style, background, or the fact that some people are just... good writers.

Non-native English speakers seem to get hit especially hard from what I've seen. Formal, structured writing that follows grammar rules closely is exactly what Turnitin flags, which feels genuinely discriminatory when you think about it.

Has anyone actually successfully challenged a Turnitin AI flag? Did your institution have any fair process for reviewing it, or did the score basically become the verdict?

Really curious how different schools are handling this because the inconsistency seems massive.