Can you guys please list a few freelancing sites where i can really sell 3D CAD models...and actually get paid
The sites SolidTweaks listed are some of the top ones and sites that I would frequently browse through myself.
Another option could be to build up your GrabCAD portfolio, or any portfolio for that matter, and market yourself around the local community with sites such as Facebook, Craigslist, etc...
You could market yourself as a freelance mechanical engineer or whichever it is you prefer, and offer your expertise to anyone that may need some assistance or help.
Here would be an example of where to find people looking for help:
Obviously change up the location to fit your needs.
Best of luck!