I had always assumed that any shofar made from a ram's horn is kosher without further investigation, but this question asks about validating the kashrut of a shofar, including this:
It seems that there is growing concern, and perhaps even some evidence, that Shofar producers are selling Shofaroth with very well disguised defects that render them not Kosher.
What kinds of defects can render a shofar not kosher? Are any of them things that can develop over time, such that I should be checking a shofar before using it?
(Note: the other question asks about verifying the kashrut of a shofar; my question is about the kashrut requirements themselves.)