Type of product or service purchased by this customer.
Large purchases, premier products or services purchased?
Easy to work with? Buys many products in one visit? How are they different from other customers?
Brainstorming tip: Are there trends in how your secondary customers lead their lives? Here's some examples of things you might have noticed that many of your secondary customers have in common: particular political beliefs, a preference for a particular grocery store (eg. walmart vs. whole foods)? Have similar family structures? Enjoy a particular hobby? Exercise habits? Dietary preferences? Religion?
Brainstorming tip: Are they famously frugal? Willing to pay for convenience? Prefer to spend their money on experiences rather than things?
Brainstorming tip: Do you know your secondary customer's preferred news source (The News Times, The Economist, etc.)? Favorite TV shows? Entertainment genre (comedy, horror, action, etc.)? What about magazines, podcasts, or websites they like to read?
Some examples might be: retail, finance, construction, manufacturing, wholesale, distributors, services.