heres my 2 cents,
first, according to law the jpj dont have the power to stop people from selling or installing performance stuff in a shop. they however can stop you once you are on the road hile using illegal parts
two, the only people who can stop the accessory and performance shop from selling stuff is the trade miniostry but they are only intrested in vcd and dvd.
three, play dirty when you know you are right. once i was stopped at a jpj road block. since my mods are considered barely legal following jpj regulations, i was let go.
here a scrip of what happened.
jpj officer: cantik kereta?
me: memang
jpj: bukak hood
so i pop the hood.
jpj: ni enjin dah register?
me: dah lama dah (in a lansi tone)
jpj: mana registration?
me: tak bawak.
jpj: mana boleh tak bawak.
me: encik gila ke? kalau orang curik kereta ni free free je bagi registration sekali.
jpj: salinan pun tak ade?
me: sama gak, pastu dia orang boleh buat original copy.
jpj: habis macam mana ni?
me: mana saya tau, bukan masaalah saya road tax baru tak ade nombor enjin.
at this time another officer had came and were checking my car, he saw the big exhaust (tip only, inside 1.8inch s-flow muffler) so asked the partner to rev my car.
he rev until redline so it was kinda loud, he looked at me and i said, cik, saya bukan bodoh. tu bukan cara nak test bunyi.
jpj: kalau camni kita tarik jelah!!
me: boleh tarik tapi bagi saya nombor staff encik supaya saya boleh bagi saman kerana menyusahkan saya bila kereta saya pass nanti.
after that was said that the two looked at each other and said, pegi lah kau, banyak lak cakapnye.
so moral of the story is, keep the mods simple and always check whether you are within the law. since some laws have gaps in them, use it. dont be affraid.