Overcast Sky is just jpg image, not HDRI so can not be used to illuminate the 3D scene. You can use it just as a background.
If you wont price $25 your image need more dynamic range and must be in HDR 32 bit format. Look at one of paguthrie HDRi, then you will understand what I’m saying. http://3docean.net/item/hdri-1554-clear-sky-low-sun/1613284
There’s nothing wrong with your picture, the price is probably less because it is a simple jpg 8bit images, not 32-bit HDR image that is often used in 3D. This is my opinion, but wait for their response and you will see why they gave such a low price.
It is best to put all these formats: HDR, EXR and jpg. Definitely You have to put hdr format, without it, 360 panorama is inefficient in any 3D program.
I moved a few months ago on a non exclusive. For now I can say that I am satisfied. Of course it is a percentage of 33% or 40% is too small, but you can sell in more places and see which one suits you better. If one place proves much better than others you can easily cross the back on the exclusivity.
I think that the quality of the models from 3D ocean meets the standards of most customers. Look a little better, and you will see that actually there are more bad 3d models on Turbosquid. There are no quality checks, you can simply put the cube on sale for $100, and nobody cares.
For me, the non exclusives seems like a better option, but it is too early to be sure.
December 2012 is my best month so far. More then 45 sales. This monthly earnings is 3 times higher than the previous months. I hope it will stay that way.
Materials and Shaders category supports a newer version of CINEMA 4D. Unfortunately, I see that supports only R14, they skipped the 12 and 13 version.
I’ve created a v-ray materials for cinema 4d r12. It is a set of ceramic tiles. Unfortunately Cinema 4D R12 not supported in materials and shaders section. Is there any hope for Cinema 4d R12 ? I’ve already spent too much time to give up.