What is the best way to make imperfections on your objects to make it look realistic. Do you need a specific plugin or another software? thanks I’ll appreciate your help. 
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If you don’t have a material with roughness map texture or you want to have something custom (for example scratches only on the corners of the object or other effect based on the shape of the model) you may be interested in the Substance Painter.
Node editor Substance Designer can do it for you as well and potentially automate some things.
Then you just import created textures and set material in Rhino. Some software has live link plugin with Substance Materials, but afaik Rhino doesn’t.