how we can know certain area of car is painted or its orignal
due to its color, shade, finishing etc
You can judge it from curves, shade, knock with hand & judge the sound (Not applicable for spray), if sounds a bit heavier than other portions means that area is affected/ dent.
would this technique on repainted (plastic) bumpers too?
bumpers are negligible even if they are repainted.. there is no proper method to check if the plastic bumper is painted or not.. Bumpers are usually not considered when checking for an original paint of the car.. so don't woory even if it is repainted.
get it checked by ur mechanic... best way
sound knocking at the bonnet & trunk will always be heavier because of mesh underneath so be aware of the fact too.
mechanic or painter???
Denter:P