There is mixed practice in how people are classifying the term "industry" related to their discussions on industry-focused searches.

What is the most common way to think about industry classification and sub-verticals in the search space? Aside from mapping out detailed NAICS and scrolling through IBIS World reports, are there any other suggested resources out there for drilling into sub-verticals and niches?

In some cases, people are referring to 'business services' as an industry. For a search focused on 'business services' -- agnostic to which industry the services are delivered into -- can anyone provide more insight into how to bring more structure to the search given this is a broad term? Are searchers more commonly finding sub-verticals and niches through in-depth top down research and sourcing or is there a better way?