I think those handicap stalls should be used ONLY for those who are physically challenged.  So how does the general public know if such person is legitimate?  HAVE DIFFERENT COLORED PLACARDS.  One color for those who cannot drive so is a passenger.  One for ailments that are physically noticeable.  One for those with heart, lung etc problems.  Then at least those who look healthy but have a heart problem won't be challenged or given the "stink eye".  My opinion.