I'm a hockey card collector myself, but obviously the American baseball card market obviously drives all aspects of the card industry.
Anyway, a few months ago I picked up a book called "Mint Condition: How Baseball Cards Became an American Obsession." It's a good book, very well-written. Chapter 11 deals with card altering, and how the grading companies are failing to detect it. This was the highlight of the book. Anyway, the guy who has been able to fake out the grading companies has a website worth looking at: