Certified coins by the two top-tiered grading services command the highest premiums in the numismatic marketplace. The Professional Coin Grading Services. The Four Major United States Coin Grading Services Are: · PCGS (Professional Coin Grading Service) was established in 1986. · NGC (Numismatic Guaranty. Top 4 Grading Services · Professional Coin Grading Service (PCGS) · Numismatic Guaranty Corporation (NGC).

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