User is notified when new content is created using Rules
It really depends on your setup. A simple way to achieve this would be to assign business users with a role let's say "Business". Once that's done you can create a trigger on creation of new node, set conditions based on your requirement e.g. user role = "Business" and category = "Plumber" and action to send out an email.

You might need additional modules if you're looking at sending out HTML emails.

Let me know if you need any help.

Thanks