SEO is such an easy thing to do, and yet since it is widely un-understood, there are a number of SEO schemes around to avoid.
Be skeptical of any SEO company that approaches you randomly via email.
These emails are likely just spam.
Further, it is impossible for an SEO to guarantee a ranking within a search engine.
Some SEOs will claim to have an arrangement with a search engine (usually Google), that will allow them to submit a "priority" listing to the search engine.
That is simply not true.
Google does not have any such relationship.
You can submit your site to Google yourself, either through their "Add URL" page or through their Google Sitemaps program.
Both of these options are free of charge, so there's no need to pay someone to do it for you.
Be wary of SEOs that offer things like link popularity schemes or ones that suggest submitting your site to thousands of search engines.
Generally, these practices don't affect your ranking in any positive way.
In fact, doing these things can have a negative effect on your ranking.
Remember, whether you do it yourself or hire a firm, it will take some time to boost your ranking up there on the first page.
Search engines can change their algorithms as often as they want, but if you keep your keyword content fresh, they will be captured and indexed by the search engine spiders.
Remember too, that search engines aren't the only visitors you want to attract.
Keep your site's content useful and interesting and you'll have a stream of repeat customers who just might spread the word around.
Just be careful, and you should be able to avoid the bulk of the SEO schemes and scams.