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T206Collector...where a little practical experience can go a long way. I've cracked a few SGC slabs in my day. Take a flat-headed screwdriver, place it into the edge at a corner and gently twist 90 degrees. Repeat at each corner and then around the edges. If done properly, it will not break the casings, just the seal. Then, try putting the the casings back together, and you will see what the frosting would look like -- it's bright silvery/white all around and looks quite different from the SGC factory seal. I am sure this process could be improved upon and that a competent scam artist could fool the best of them.
In the end, you have to use third-party grading for what it is best used for: adding another indicia of card quality, along with information about the seller, the context in which the card is sold, and, most importantly, your own personal experience reviewing cards and confirming the SGC grade.