The book Start Small, Stay Small, gives examples of this, as well as ideas on finding niche markets. Interesting and useful stuff. You may locate a niche mark

The book Start Small, Stay Small, gives examples of this, as well as ideas on finding niche markets. Interesting and useful stuff. You may locate a niche market, find that there is genuine interest in it as reflected in ad words, and also get a sense for what the existing market is like (e.g., is there already a highly-dominate player, and is it cost-effective to try to move into this niche).