In this paper about "Nigerian" mail fraud http://research.microsoft.com/pubs/167719/whyfromnigeria.pdf
researchers argue that it's very efficient for attackers to appear fraudulent, because this helps select the most gullible victims (true positives) while weeding out "false positives": people who respond at first, but are not scammed in the end.
From the abstract:
> "Far-fetched tales of West African riches strike most as comical. Our analysis suggests that is an advantage to the attacker, not a disadvantage. Since his attack has a low density of victims the Nigerian scammer has an over-riding need to reduce false positives. By sending an email that repels all but the most gullible the scammer gets the most promising marks to self-select, and tilts the true to false positive ratio in his favor."
Shouldn't marketers do the same? Isn't it more efficient to eliminate non-targets as early as possible, instead of dragging into the process people who will ultimately relent. If so, it would seem preferable to send junk mail that is very explicitly junky.