Being overcharged for medical services isn't peculiar to foreigners. Thais get ripped off too. I knew a woman whose dog bit her at home, just nipped her really but enough to draw blood. At the hospital, they insisted she have the full treatment: full series of rabies shots, antibiotics, bandaging, etc. And the elderly in Thailand are the favorite target of scammers just as they are everywhere. I think your problem may be more with modern society rather than anything personal.