Don't just swallow anything they throw at you! Мало ли какие слухи про нее ходят...
I assume the sentence means:
You never know / Who knows what kind of (unreliable) gossip may be circling around about it.
I'm having a hard time wrapping my head around why the adverb "мало / little" coupled with the interrogative particle "ли" gets to have this meaning. Can I interpret it as:
What kind of gossip may be circling around – Do we know even (a) little about it?!
What kind of gossip may be circling around – Just how little do we know about it?!
What kind of gossip may be circling around – We know so little about it, don't we?
... asking in a rhetorical fashion? I wonder if some verb like "знать" is omitted?