If people are already on a search engine about "cigarettes" they are more likely to be interested in buying marlboro cigarettes than a general search on a larger engine which has marlboro in it. This additional targeting is frequently available at little to no extra cost...sometimes even less than the costs at general search engines since there is less distribution and fewer competitors. Using these search engines you can target specific industries or locations easily.
The one bit of caution I must throw to the wind is that some sites bid on their own other sites to artificially inflate click prices (see MadamTobacco). If you look hard it is easy to find reputable niche specific PPC search engines, typically they will have more advertisers and look more professional. I think MadamTobacco does not look very appealing
a few examples of good PPC search engines
[Edited so the links aren't clickable. - Jill]
Edited by awall19, 10 August 2003 - 03:11 PM.