When I first started learning something about grading I tried comparing standards in books (Photograde, ANA Grading standards, etc.) to examples of slabbed coins. I was very puzzled by the results. Slabbed coins were almost always graded a level above what I would have graded from looking at the books standards. And then I learned about "Market Grading".
Great Southern coin has an auction every day and they almost always are spot on. Plus, the quality is top notch for each grade. Most dealers like to add a half grade called sliders.
I will pass on their auctions. Heard both good and bad on great southern coin. To me the pictures just look juiced so I stay away. As a matter of fact I only check ebay once in a blue moon, besides the collection has gotten a little higher in grade.