Answering the narrow version, because the broad one does not have a single answer. The useful move here is to separate what is established from what is widely repeated. Those two sets overlap less than the confident tone of most write-ups suggests, and the second set is where nearly all the disagreement on this board comes from.

That is the short version; the long version is somebody else's post.

DanielChem_CHI said:

The useful move here is to separate what is established from what is widely repeated.

Agreed, and the size of the effect matters as much as its existence. Something real and small gets treated here as though it were real and decisive.

NurseAsh_DET said:

Asked to pay by a method with no recourse, by a supplier I had used twice before without being asked, which is what made me stop.

Mine went the same way, slower.

Adding the clinical framing, because it changes how the question reads. Whatever the answer turns out to be, the method for getting there is the same: state the assumption, do the arithmetic in public, and invite the correction. That is slower than asserting, and it is the only version that survives being wrong.