Choosing a Marketer
There are many levels of search engine marketing offerings available.
Basic submission services, i.e.. Advertising $59 submissions to the search engines, are people to stay away from. Search engines do not appreciate continual submissions - you only need to let them know once that your site is live. It is not necessary to submit your site to thousands of search engines. Remember that over 90% of all searches are performed on Google, MSN, Yahoo and AOL.
Search engine optimization companies that specialize in "ethical" optimization (there goes that terminology again) are good choices. By ethical optimization, I mean that they will use your Web site, will make changes to programming, design and/or content, and will work with you towards your site goals.
Search engine marketers will often combine the ethical optimization approach with keyword buying and link building.
Some search engine professionals use practices that may be considered spam by the search engines, if they get caught. Whenever someone tells you that your site will not have to be changed (and you know that you are having positioning problems), or promises a guarantee, you should be careful. If your site does not have to be changed, it may imply cloaking, or perhaps doorway pages. Today's doorway pages are not the bulky, text only pages of a few years ago or a quick redirect. They often resemble the site very closely, and may be worked into the site, but if the page is not part of the site, it is still considered a doorway page.
No one should promise you a top 3 organic search position on the search engines for a generic type keyword. And if you are told by the marketer that they "know the search engine's algorithm", don't believe it. And if they say that people don't get banned from search engines for spam practices, don't believe that either.
Build your site right, with relevant content that your visitors want to see, and your site will do well on the search engines, without the worries or concerns that your site will be banned from the search engines.
Resources:
Other links relating to ethical search engine marketing:
Searchenginewatch.com article by Danny Sullivan