*Costs*
The primary disadvantage of paid inclusion is the cost, although this factor naturally depends on your means. Typically, submitting to a few paid programs would cost anywhere around $1000 a year.
*Reach*
A second disadvantage, perhaps more accurately described as a limitation, is that Google does not offer paid inclusion (and maintains that it never will). Since Google currently provides the primary results for three of the top four engines (Google, Yahoo, and AOL), engines that offer paid inclusion may only account for a fraction of your overall site traffic. Google typically updates about once every month, and there is no way to add your pages to their index any faster- which means that you will be waiting for Google to index your new (or newly optimized) pages regardless of which paid inclusion programs you use. Only after Google lists your pages will they appear in Yahoo and AOL results.
*Considerations*There are many factors to consider when examining paid URL inclusion. The following five are some of the most common:

*Are my pages already in the index?*

Just because you can’t find your pages when you enter search terms does not mean that your pages haven’t been indexed. To see if your pages have been indexed, go to the engine and search for each of your exact page URLs in quotes. If each page shows up for the URL search but not for a search of any key phrases related to the page, paid inclusion will not help your rankings (your pages are already in the index and have been ranked according to their perceived value). It would be much more beneficial to invest some time and/or money in optimizing your pages for better rankings (you can still consider paid inclusion afterwards if you don’t want to wait for the spider to revisit).
*Is it a good investment for me?*
Naturally, budgetary constraints can be a primary consideration. If you can’t afford paid inclusion, then it obviously isn’t an option. However, simply because you can afford it does not mean it is a good investment. For example, a business that sells a very inexpensive product online that is counting on volumes of traffic may not see a good return on their investment (again, 3 of the top 4 engines do not offer paid URL inclusion). On the other hand, if your business has a high average dollar sale and you put a high value on each quality lead, you might consider immediate paid URL inclusion a no-brainer.

*Do my pages change frequently?*

If your web pages are subject to daily or weekly changes in content, paid inclusion may offer some additional benefits. When your pages are spidered frequently, all new content is indexed by the engine soon after it is added to your pages. This means that your pages will begin to appear in searches for terms related to the new content much more quickly.
Are my important pages dynamically generated?
Some search engine spiders have a problem finding and indexing pages that are dynamically generated (such pages often have a question mark somewhere in the URL). By paying to include the important pages of your dynamically generated website, you can be sure that they are in the engine’s index, even if the “organic” spider would never find them on its own.