Yes agreed KL has the worst taxi service and 2nd is Sillypore! Called LTA's so called "complain hotline" so many times - totally USELESS!!!
Bangkok as long u dun take the taxis loitering outside your hotels or at tourist attractions you are safe. So far in my 15 years traveling to Bangkok only kana scammed once, meter was rigged, from airport to my apartment usually Bht230-250 but that day was like extra Bht100!