Markus,
 
I agree with your bowling theories completely.  I also agree with Peta
about murex -- they are well worth collecting.  My problem is I have
seen very few shells I don't like.  Even the supposed ugly ones are
worth it for their character.
 
In fact, in front of me on the desk is a really beaten up Conus
delessertii that had three rough, lip destroying encounters.  Dealers
would not even list this guy as F-----.  But the color is good and the
remarkable efforts the animal went through to heal these breaches make
it so interesting I keep it around to marvel at.  For anyone even
slightly interested in why a shell gets broken and how it copes I
recommend Vermeij, Geerat J.  "A Natural History of Shells."  After
reading his book you may be a bit slower to discard that less than
perfect shell.  Or maybe not.
 
Tom Eichhorst in New Mexico, USA