Checking bats? what to do?

[rbmartin]

I was working a tourney a few weeks ago (cal ripkin/obr rules). After a batter rocketed one off the wall, defensive coach asked me to "check the bat". I examined the bat (an Anderson Tech-zilla if I recall correctly). All proper markings, proper size, no signs of tampering, no mystery objects rolling around inside, ball sounded normal leaving the bat. I told coach "bats fine" and we played on.

My question is, what type of things should I be looking for when asked to check a bat? What are some things you more experienced guys have seen over the years that I should look for during bat inspection? Should I educate myself as to the style and construction of common bats so I can better spot an altered one?