I noticed that you're using a method I myself once tried, it is really hard to get good looking, and if you paste reflections from a background like that, then you should use the background you took the reflections from.
@ Vicent M : The reason for those paintjobs being so "flat" with minimum reflections is because of the photography techniqes used, so it doesn't work that way with all natural light, that result is achieved by either lightpainting the car, or using a flash, but on a black car with only the available light, like the streetlights that seem to reflect, the car will be that shiny, so it's all about what kind of result he wants to achieve
Also, black shiny paint basicly is dark chrome, even with lightpainting and flashes it would look more shiny than the ones you gave as an example
( if he's not aiming for metallic black or a surrealistic result)
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