Many words that are similar carry very different meanings, but that doesn’t stop people from misusing them. Generally, they’ll accept a correction in the intended spirit, but that isn’t always the case.
I remember one situation in which a client was so convinced that his misunderstanding was actually correct that I lost his business. He ran a company in human resources, and I had used the phrase “to complement your staff” in an ad. He changed it to “compliment.” I changed it back, and he responded with fury.
He screamed at my graphic designer partner, stating that I must be an idiot who couldn’t spell. The designer called me, and I explained that “complement” and “compliment” are two entirely different words, and that in this usage, “complement” was the correct one. It wasn’t a matter of personal preference, but one of accuracy.
The client insisted that “complement” was a non-word that wasn’t part of the English language. Even after being presented with a dictionary excerpt, he continued to insist that I was wrong and that it wasn’t a word. The ad ran, and we never worked together again.
Part of my responsibility as a copywriter is ensuring that a client is presented in the most favorable light, and making sure that the right words are used is a critical element of that. I’ve argued with clients over other words and punctuation. Sometimes, the clients thought I was simply being difficult. But all I was doing was protecting them by ensuring that they appeared to be intelligent and literate. I wanted them to earn compliments for my work, and yes, that’s with an I.