When purchasing a Shofar, is it necessary to look for a 'hechsher' to ensure that it was manufactured properly (e.g, no cracks), or can its suitability be determined just by visual examination?
Even if the horn comes from a kosher animal, the shofar could still be rendered non-kosher if non-kosher materials are added during the shaping and polishing process. According to this article (http://www.jdoorpost.com/2010/06/non-kosher-shofars-imported/), there were problems last year with shofars from China and Morocco.
Apparently, you can hide cracks. See this.