Someone can feel free to correct me on this but he wouldn't be breaking any laws by selling you a standard lower (no BB).
After all it could be for a rimfire build, which doesn't need one. Our you could be planning on going feature-less. YOU would have to install a BB before mating it to a centerfire upper otherwise you would be in violation of the CA AWB.
Mine came without a BB.
Sent from my Galaxy Nexus using Tapatalk 2