I share zeOrb’s opinion. Why would I, or anyone in that matter, want to buy a character, something which is supposed to be animated in someway, without the necessary rig? For me that’s like half of the product is missing and has no use for me.
I would go as far as saying that if you are specifically talking about characters you have to follow Epic’s guidelines. There is a section which would apply called “Skeletal mesh requirements”. Link (scroll down to the section). Otherwise your content is most likely (or even guaranteed) to be rejected.
Also, I don’t think you can rig a character within the engine. You can re-target animations, add sockets, but I never heard of someone creating a rig within the engine. That’s something which is, to my knowledge, only possible outside the, or any(?), engine and within the modelling program itself (Maya, 3ds Max, Modo, Houdini, Blender or whatever you use).
Greetings,
Dakraid