the whole "andalite bandit" thing is actually pretty laughable when you take step back and look at it. because when you compare the animorphs' actions to the way that andalites actually act - they don't really do that good a job of selling it. "if we never talk, we won't give them any hints we're human!" meanwhile every single andalite who comes face-to-face with visser three immediately starts cursing him out. "let's fight them with earth animals!" as if any self-respecting andalite warrior (ax included) wouldn't just use his tail blade given the opportunity. "we must never let them see us demorph!" the andalites have basically no reason to worry about hiding their identities - as far as they're concerned, there's no way the yeerks could ever hurt them in a way that matters, anyway.
and the biggest irony of it is that visser three is the single yeerk who should have the easiest time seeing through this, seeing as how he is the yeerk's foremost expert on andalite behavior even ignoring the fact that he is currently infesting one, but he's such an arrogant blowhard that once he gets the idea of "andalite bandits" into his head he absolutely refuses to entertain the notion that he's wrong.