IMO it really just comes down to experience. The more cards you have looked at to see why the card graded such and such the better you will become at accurately grading the card before submitting. If you have only looked at 100 cards, you're not going to have the same eye as someone who is looking at a 100+ cards everyday. You really can't cheat that experience.
Also graders are kind of like meteorologists, they can be off 50% of the time and still keep their job.
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Current Wantlist:
E92 Nadja - Bescher, Bridwell, Cobb, Donovan, Doolan, Doyle (with bat), Lobert, Mathewson, Miller (fielding), Tinker, Wagner (throwing), Zimmerman
E/T Young Backrun - Need E90-1, T216 (all versions)
E92 Red Crofts - Anyone especially Barry, Shean, and Evers
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