If you are writing for print media, you are not likely to be asked to provide an unpaid sample article written specifically for a potential client. Free custom articles, however, seem to be a common request for online writing gigs. Should you write a free sample article if it is requested?
There are magazines and websites dedicated to B2B topics that you’ll never hear of if you don’t look. These can be great places to sell article ideas if you can take the time to understand what they need.
If you find yourself writing for the same niche over and over, it will save you time and effort to build a database of information and industry sources that you can access on demand.