Inspired by this comment, there are Chazaka's (presumptions) and principles of נאמנות (trustworthiness) in Halacha that no longer hold in our practical experience.
One example is עד אחד נאמנן באיסורים. As linked there, if someone isn't under suspicion (and it is an aveira to be חשד בכשרים) their statements about their Kashrus should be believed. On the other hand, centuries* of practical experience has shown us that when someone has a financial incentive there is not an insignificant chance that they will lie (e.g.) especially when the financial stakes are high. Also, I have seen a lot of just downright ignorance in believing something to be Kosher, and perhaps claims of something being Kosher based more on a failure to do due diligence rather than real dishonesty.
Another is example is חזקה אין אדם מעיז פניו בפני בעל חובו, where anyone involved in a Beis Din cases that I have spoken with says that the bald face lying in front of a creditor is rampant. Although this particular one is a bit different, as it functions to makes us more suspicious of the borrower, not less (perhaps his credible sounding claims are lies because he doesn't want to lie all the way, even if he is inclined to lie), so it is hard to apply an observation that borrowers are more dishonest to establish their credibility.
So how do we approach this observation in differences between the framework of Halacha and our present day observations?
*A very big Talmid Chacham involved in Kashrus told me that there were takkanos in Europe going back a couple of hundred years at least to require retail food sellers to have certification because of this problem.