Masking is the essence of blending 3D models and painting together. In my work, I've learned methods of masking that eliminates any gaps or overlays, making a seamless set of layers that you can use to control the colors and patterns in your product without the tedious labor of masking off each section of your product image.
For example let's say you have a shirt you want to post on your website, but you don't want to have to re-shoot the product on a model for each color. I can mask off the sections that are different colors and keep each mask on a separate layer, giving you control over the color and pattern.
If you need to do this and can't do it yourself, once the masking is done it's simple enough for me to do the color/texture changes myself for an affordable fee.