I think that no amount of verification or technical details would satisfy you, because you could simply turn around and say, "well that might have been the case on the day is was verified, but what about the day after?" or "why should we trust the independent auditor?" In other words, you are just trolling. If you are the one claiming they are not trustworthy, despite them having an almost flawless reputation, then the onus is on you to provide evidence to back up your claims, not the other way around.