How to package a model to sell?

The most popular file formats on CGT currently are still .max (3dsmax) or .ma (Maya). However, Blender is gaining popularity as well. Just be sure you offer FBX and OBJ along with it. As for the .blend file format, I think PhantomDesign covered everything regarding textures. However, Blender offers the unique ability to pack all external data into the .blend file, and this also includes textures. You will still need to include the textures in a folder for your other file types like OBJ, and I would include them anyway, but I usually pack all textures into the .blend file so there's no confusion or user-end problems when opening the file. It may reduce user-end errors and complaints when it comes to texture maps, etc. Just go to File > External Data > Pack All Into Blend if you want to do this. Keep in mind, it will increase the file size fo the blend because every external file will now be contained in the .blend itself. I've found it's a good way to distribute a Blender file.

When you finish model , set it up as you like (you can upload model w/wo material setup , w/wo textures etc.) If you have textures, create single folder, in that folder create another folder named textures and put all textures there. In blender applay textures (from that "texture" folder) onto the model in such way that when you open .blend file textures are automaticly loaded and applied onto the model, save model as .blend in that same folder where texture folder is. Than using winzip or winrar zip texture folder and .blend file. This zip file you upload here as model in it's native format in this case blender. Repeat this for every format you can get out of blender that's not problematic (obj, fbx, dae etc etc). Problematic= bad normas, bad scale, unnesecery triangulation etc. Render some preview images for presentation here on cgt but I think that's self explanatory. I'm not a blender guy but I think principle is the same. Good luck.