I think the right line to draw is: "Would the general public be surprised that this cost is included, or by its magnitude, or by the impact on price paid by buy

I think the right line to draw is: "Would the general public be surprised that this cost is included, or by its magnitude, or by the impact on price paid by buyer or price received by seller as compared to other payment or purchasing methods?" Or, looking at this from another angle, "Is there a widely applicable ban on disclosing the fees which is in practice harming the ability of consumers to make properly informed purchasing decisions?" There's no way to draw a perfect line between forced disclosure for transparency purposes and respecting the right of companies to set their own policies. But I'm okay with imperfection, since that's all that reality offers.