I haven't really personally used Google+ for business purposes. I don't think it is the best available option. There are so many other, much more popular social media platforms, such as: Facebook, Twitter, LinkedIn, Instagram and more. Google+ can be a bit hard to use as efficiently as others.
Regarding on how to check if somebody blocked you on Google+, the only real way to tell is that when you try and view a person's profile you will see an option that says ''RESTRICTED''. That is the best way to tell... another way is the fact that you won't be able to mention them in your posts. Clearly, if they block you, you won't be able to see any of their posts either.
Hope that this was helpful