Quite literally, there is today a not-so-insubtantial push against over reliance of Athenian sources in Greek history. Which is inconvenient, because especially for classical and archaic Greece, nearly all our contemporary written sources are Athenian.

That said, most of it probably isn't lies. Hearsay yes. Biased yes. But even Herodotus engaged more than once in telling a story in his work and then gave a long explanation of why he didn't think it was true. The standards might have been much looser then, but there's not always an explicit reason to think ancient writers were outright lying.

They were just telling the story from their own POV, with their own sense of how the world worked and what was or wasn't true.