"There will always be a market for...."

For a while after the Soviet Union fell, "USSR invades America" novels were still appearing in bookstores. I doubt they sold well. As for the ones almost ready for submission....

On the other hand, some Warsaw businesspeople used their new freedom to sell an exotic American delicacy -- bagels.

It pays to keep track of trends which might affect your product. A couple of suggested sources:
http://sciencedaily.com
http://politicalwire.com
reprinted from freelancersunion.org, Twin Cities After Hours Hive