Google penalizing sites for certain keywords?

Hello, new to the forums. I've been teaching myself SEO in my spare time for the past couple of months and recently started working for a hookah company working on thier website and helping them with their SEO.

When I fist started here the site was in Google's top 10 for the search term "Hookah", but after a few months of updating and adding to the sites content it dropped to around page 11 and then not long after can't be found anywhere as far back as page 50. All I've really done is add content and make existing content more professional while sprinkling in hookah related keywords.

Longer tailed keywords still appear in either the top 10 or at least in the first 3 pages, but our site is nowhere to be found for the most important keyword anymore...

My question is what could possibly cause this? Has anyone ever had this happen before? If so, anyone know of any good suggestions for fixing it? I've already done a ton of searching on this matter and haven't turned up anything...

yeah, that's what the site owner said too, but it's been over a month now and no change.

The link building is originally what I thought might be causing it. The owner actually has a team of people in India that take care of the link building. All I know is that they do some link purchasing and when I asked if any of it could be black hat he assured me they only bought good links with high PR.

Even so, why would it only affect one keyword? Wouldn't that lower your ranking for everything?

No, not if they were focusing on your main keyword. I did a link building campaign focusing on my main keyword, and went from page 2 on Google to page nowhere... I mean not in 1000 search results, but only for that one keyword, every other one stayed the same. I freaked, but in the end what could i do? Read up on it, but in the end, just kept plugging away, and in about two weeks I showed back up on high page 3. (now I'm 16)

If you want to pm me with the url, I'll take a look at it for you see what I can see

Maybe the competition has upped their efforts too?

Google watches high volume and high cpc keywords but not all. This keyword may fit so it has this special experience.