This is a great article to detect non-random shuffling machine. Especially table #1.
http://www.borisbj21.com/Page8/page8a.html
This is a very old article. The casinos which I suspect clumping the shoes have even worse statistics than the numbers on the right side of the table. Basic Strategy players are severely hurt by the clump. Examine these numbers, have them in your mind and comprehend the meanings they have to the game. Next time you play Blackjack, think of them.