buckworks - 3:56 pm on Dec 28, 2008 (gmt 0)

no 'ethical' way that site B can conceivably come out on top in the serps

Sweeping generalizations are a logical fallacy.

Site B wouldn't need to come out "on top" to gain useful exposure.

The ethics of tactics that might nudge his site into the top ten for an absent keyword would depend a great deal on what the target phrase happened to be.

However, the efficiency of such tactics would be open to question no matter what the target phrase.

Depriving site A of a visitor

Not necessarily. Many searchers check out more than one site.

Diverting the visitor from an expressed choice of site

Again, not necessarily.

Distorting the serps, potentially damaging users' faith in the SE.

Again, not necessarily. A great deal would depend on relevance. In this case Site B thinks that users would find his products to be strongly relevant. That might be realistic or it might be wishful thinking.

Quadrille, it's worth noting that your list of concerns would also apply to AdWords.

In my opinion the ethical essential for Site B would be to write a crystal clear <TITLE> and meta description so users who saw his link in an unexpected SERP would have an accurate idea what to expect if they clicked. Beyond that, ethical questions would depend on the details.

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The idea of ranking for an absent keyword is theoretically possible, and superficially attractive, but Site B needs to look at the idea with hard practical eyes.

-- What else would have to be given up in order to achieve that?
-- How productive would it be, really? No wishful thinking allowed!
-- What else could be achieved if the same promotional energy were harnessed in more conventional ways?
-- What could go wrong?
-- ___________________

Beware of unintended side effects. It would not be a step forward for Site B to gain the ability to rank for for "Acme Company" if in the process he messed up his ability to rank for "blue widgets".