You can never fully determine whether a post was written by AI, and that's unlikely to change. The most you can do is look for statistical patterns across a user's post history. Do they consistently use em dashes? Are their apostrophes always typographically "smart"? ChatGPT, for instance, outputs curly apostrophes by default, which is a subtle but sometimes detectable tell.
But even that only gets you so far. No detection method can be both precise and reliable at the same time, you'll always be trading off false positives against false negatives. Flag too aggressively and you'll wrongly accuse genuine human writers. Be too lenient and bots slip through. Some people naturally write in a structured, formal, almost clinical style, the kind that AI detectors associate with generated text. Others have been writing on the internet long enough to have absorbed those patterns organically.
Formatting heuristics suffer the same problem. Bullet points, numbered lists, hedged language, and balanced paragraph lengths are common AI tells, but they're also just... good writing habits. You can't penalize someone for being organized.
Also, I wanted to point out that equating AI-generated with low quality is a flawed premise. Humans write poor posts all the time, and someone who uses AI as a drafting tool but actually reviews and edits the output can produce something genuinely valuable. What people really object to isn't the quality, it's the lack of authentic engagement. Those are two different things, and conflating them leads to exactly the kind of false assumptions that get real humans flagged as bots.
