I do not take their claims un-skeptically. I've been lied to one too many times by users who claim, "Oh I totally didn't do anything to get banned, bro."
But I don't trust you either, and my reasons for being reluctant to flag and downvote are genuine. This is because I've also seen moderation teams who swear up and down that they're not biased, but who later get caught out when they put their finger on the scale through action or deliberate inaction.
But there's another dimension to the unfrustworthiness, because I have also seen moderation teams who don't put their finger on the scale per se, but are so invested in their own rules that they let their community rot beneath their feet from people who have figured out how to manipulate them.