At times I too had been asked to write samples. All I do at that time is, show them my Ezine link and ask them to check the authenticity of my writing style. I also mention to get back to me if they have 'NO MORE QUERIES' but article subjects and keywords. Most of the times, it works. But, at times, I do not get a response. Then, as a matter of courtesy, I send them a PM stating "All the best".
I was wondering how to avoid that. I'm quite green in the internet articles sales market, and have lost a couple samples recently. People don't usually do that kind of thing when you work face to face with them and meet them on a regular basis. I really liked the post-the-free-sample-in-my-own-blog approach, I think it's the most useful piece of advice, as you are building the portfolio and giving the sample they ask for without giving it away. That should satisfy anyone, as some usually ask for niche-specific articles to measure performance, which they get to do.