Be wary of SEO (Search Engine Optimsation) firms that send you email out of the blue promising to rank your website highly in search engines.

A lot of the time, these "firms" will do your website more harm than good, for example by using shadow domains and doorway pages.

Serious SEO firms will not send unexpected e-mails, advertising their service. If you need an SEO specialist to work on your search engine rankings, you may want to do some reasearch on the SEO industry and seek out a serious, legitimate company yourself.

There are a lot of factors to consider when choosing an SEO firm. Some good points on this subject are made on Google.com:
http://www.google.com/support/webmasters/bin/answer.py?answer=35291

In any case, trust your instincts first!