That's not an SEO challenge; that's a math problem: searches x marketshare = visitors

I responded with a few factors that override mathematics in SEO game, including site's title tag and description tag, as well as whether term lends itself to scrolling. I also pointed out that it depends on title tags and description tags of competition, too.

Another factor that makes predicting traffic difficult is abandonment factor – how many people click on none of results because they get interrupted or confused, or abandon search for a new one because they find themselves off-topic or searching too broadly.

It also depends on how many sponsored links there are and how they are marked. Often at Yahoo and Lycos, for example, there are so many ads that average searcher might never scroll a screen or two to see organic (natural) results.

And, of course, it also depends on color of walls in room searcher is clicking from, weather outside and how well they slept last night. But there is little you can do about that.

What you can do is to work with your SEO consultant to choose most effective search terms for your business and make sure he develops a title tag and description tag that sell to both humans and search engines. Then make sure he is monitoring not just rankings for your key search terms, but also description used by each of search engines.

A good ranking at Google and Yahoo is just one measure of your SEO consultant's success. A more complete evaluation is that he is your partner in building long-term, targeted traffic