A few weeks ago, I noticed a Facebook request for a recommended sales book to help an entry-level landscape designer find her way with clients. My first thought was that nobody learns to sell from a book. This brought back memories from my struggles as a technical sales representative just after college.

I was primarily hired for my chemistry background, but because I had also earned an MBA, they presumed I also knew how to sell.

I didn’t, and that started my search for books on selling.

None of them helped much because selling is something you learn by doing. Thankfully, a colleague invited me to join him at a Zig Ziglar selling conference that changed my life. Zig mostly taught the soft selling skills: how to listen, clarify buying needs and wants and get customers to like you. Zig used stories from his career to show audiences how he unlocked the secrets to selling.

What then is the best sales training book?

It’s the one you compile from your successes with your clients, what worked, what didn’t work and how to do better next time. Debriefing and documenting your failures and successes is an invaluable growth practice that doubles as team building and training.

These case studies become assets that can shape your culture if they are captured before they get fuzzy or lost forever. The best, easiest and cheapest sales training comes from real customers. Here’s how to get started:

A simple case study template:

• About the client
• The problem
• Engagement details
• The solution
• Results
• Memorable quotes
• Lessons learned

It should take less than an hour to create a case study. This doesn’t have to be done with every deal, but if your price points are high, you probably should because the lessons are many. Not only does it make you better for that client, but you’ll also become more aware of keywords that will inform your sales and marketing.

Once in a while, a client’s perspective will refine your core marketing message, as it did for Jim Koch. Koch is the founder of the Boston Brewing Company and Sam Adams Beer. During the early stages of his business, Koch researched by talking with beer drinkers in bars. Once he noticed a man drinking a Heineken, at that time one of the popular imports, and he wanted to know why.

After listening to the man, Koch shared the story of Sam Adams and how he personally tested every batch. To this, the man replied, “It sounds like your beer is almost homemade, like it’s handcrafted.” That conversation not only helped to put Sam Adams on the map, it also rebranded what was formerly known as microbrewing. It’s better known today as the craft brewing industry, the fastest-growing segment of the industry for decades.

Gems like these are embedded within your customer stories, but you have to get in there to dig them out.

Talk to clients. Listen, really listen, to their words. Document that magic and use it to grow.