Rejecting Fatwas as a Layman
It is not out of place for you as a layman to reject a fatwa by a mujtahid if it is clear that the fatwa’s conclusion is based significantly on wrong dunya-related information.
For example, if you are very well informed about how a certain process works in conventional banks in a particular country, and then you see a fatwa assuming otherwise, you may reject that fatwa’s applicability in your country. It is not arrogant or out of place for you to say that your knowledge of this dunya-related matter is better informed than the Mujtahid passing the fatwa who may have been misinformed by someone else about the situation or whose fatwa does not apply in your country.
Another example is that you may see a scholar saying that it is okay to say Merry Christmas because it supposedly no longer has any religious connotations; however, you know that this is wrong because acknowledged research findings say otherwise in your country (e.g., https://www.deseret.com/2016/12/21/20602811/is-christmas-still-a-religious-holiday). In this case, you can totally reject this fatwa as invalid; not on the grounds that you’re more knowledgeable about fiqh than this scholar, but rather because you are better informed of this dunya-related matter than this scholar who might have been misinformed by others about the reality on the ground. [note: this is not the only factor to consider in a “Merry Christmas” fatwa; I am just giving an example].
Other examples could be provided; however, I think the point is clear in that it is okay to reject religious verdicts as invalid in those cases where the verdict significantly relies on what you believe to be incorrect dunya-related knowledge. And by “dunya-related knowledge,” I mean something factually measurable and not your personal and subjective interpretation of worldly affairs. One must ensure that his dunya-related knowledge is certainly accurate before disputing the secondary sources the scholar utilized or perhaps even obtained first-hand.