Anyone here sells design assets (2D/3D) on the web for extra income?

I'm looking into selling simple pieces of 3D assets on sites like turbosquid etc, and was wondering if anyone has done similar stuff before? It doesn't have to be 3D, it could be selling photos on Shutterstock / Dreamstime, or selling mockup templates on GraphicRiver etc. I'm thinking of doing this for extra side income, but I believe it's hard to make any $ out of this? Would love to hear some opinions. I'm thinking of doing a series / collection of 3D assets in a certain style.

Great design resource

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