When I noticed a mistake (circled in the image below) on the first page of a textbook titled Proofreading & Editing Precision, I thought it was a test. I had spotted it, I thought—a blooper the author had intentionally planted in the preface as a teaching lesson. At the end of the section would be a challenge for the student: “Did you spot the error? After reading this book, you will be a better proofreader and editor.” I would be ready to say yes, I spotted the error; I’m ahead of the curve.
But no such question was there. When I realized that the mistake I’d found was not a skill test but an error, my impression of the book changed in an instant. I had lost some trust in the book’s authority. Every lesson the author aimed to teach would have a bit less credibility.
If any serious textbook went to press with an obvious mistake in the second paragraph—especially a textbook on the very subject of proofreading and editing—the book would deserve to lose some of the trust of careful readers.
The same idea applies to business proposals. When a professional services firm offers to assemble a team of experts to develop and implement a complex solution for a client who is expected to pay tens or hundreds of thousands of dollars for the service, the firm should express ideas correctly in its written proposal. Thoughts should be well organized, sentences should be well structured, and yes, pronouns and apostrophes should be used properly. Anything less deserves to be met with suspicions of incompetence.