The giveaway is almost always an over-dependence on "Not 'x' but 'y'" structure. Even when the author changes the wording so that the phrase doesn't read exactly like that, they tend to leave the structure intact, and the bots really like to lead with the inverse of what the author wants to say to create contrast.

A human author might have used this technique once to really emphasize a strong point, but today's LLMs use it so often that it loses its emphasis, and instead becomes a distinct stylistic fingerprint.