It’s difficult to find any system that everyone would agree was fair. Take the Senior Citizen scenario where prices are fixed: sometimes they get half price, sometimes just a pound or two off full price, sometimes no reduction at all. Or they may be invited to be honest and only claim a reduced fee if they are only on state pension, but pay full price if they have an occupational pension as well. Then there are sometimes further reductions for disability - but do you have to show proof of disability? And your carer might go free too.
I think that, on balance, I would prefer to just be told what the price is and be done with it: then decide whether I want to pay that price or do without, rather than have to search my conscience on what I should be paying.