I definitely noticed that different industries produced different results. Some business models are very hard to define in terms of KW's themselves and sometimes search volumes are so low that you just can't capture enough interest.

In that kind of situation, banner advertising or using the content network might be much more worthwhile.

I think one of the major problems SEO / PPC companies make is that they use too much industry jargon on their landing pages. Many businesses do not understanding the terminology understandably and therefore you can only really apply to a small minority.

Explain it in business sense profit for small amount of money and you might have more success.