Common Grading Mistakes and How to Avoid Them

Why Grading Mistakes Are Costly

Overgrading a coin by even one point can mean overpaying by hundreds of dollars. Undergrading means selling coins for less than they're worth. Here are the most common grading mistakes and how to avoid each one.

Mistake 1: Confusing Weak Strike with Wear

A weakly struck coin can look circulated even in Mint State. The key difference: wear creates flat, smooth surfaces while weak strike creates soft, mushy detail that still has luster in the recesses. Always check for luster before concluding a coin is worn.

Mistake 2: Overgrading Due to Wishful Thinking

The most universal mistake. Collectors naturally want their coins to be worth more. Combat this by grading before you look up prices. Write down your grade assessment, then check — tracking accuracy over time builds honest calibration.

Mistake 3: Ignoring Problems

Scratches, rim dings, environmental damage, and old cleaning are "problems" that prevent coins from receiving straight numeric grades from PCGS and NGC. Learn to identify:

• Cleaning — Unnatural brightness, hairlines in parallel patterns, whizzed surfaces.
• Artificial toning — Toning that looks too uniform, too vivid, or doesn't match the coin's storage history.
• Tooling — Re-engraved details, smoothed fields, added mint marks.
• Environmental damage — Corrosion, verdigris (green deposits on copper), spots from moisture exposure.

Mistake 4: Grading from Photos Only

Photos can hide hairlines, make luster look better or worse, and distort color. High-quality photos are useful for initial evaluation, but always examine important coins in hand before finalizing a grade assessment or purchase.

Mistake 5: Not Knowing the Coin Type

Each coin type wears differently and has different grading focal points. A Morgan dollar and a Walking Liberty half dollar are graded differently even at the same numerical grade. Study the specific grading guides for each series you collect.

Mistake 6: Ignoring the Reverse

Many collectors focus exclusively on the obverse. Both PCGS and NGC grade the whole coin. A coin with an MS-65 obverse and an MS-62 reverse will grade in the MS-63 to MS-64 range. Always flip the coin and evaluate both sides.

Mistake 7: Using Wrong Lighting

Overhead fluorescent lighting washes out details and hides contact marks. A single-point light source (halogen or LED desk lamp) at a 45-degree angle is essential for accurate grading. Rotate the coin slowly to reveal marks and assess luster quality.

Mistake 8: Comparing to the Wrong Standard

Don't compare a 1921 Morgan dollar to a 2024 American Silver Eagle. Modern coins are struck with vastly superior technology and come from the mint in much better condition. Grade within the context of the coin's era, series, and typical surviving condition.

How to Calibrate Your Grading Eye

1. Study PCGS CoinFacts and NGC Coin Explorer — Both provide photos of coins at every grade for most series. Study these systematically.
2. Handle graded coins — At coin shows, ask dealers to show you examples at different grades. Compare in hand.
3. Grade blind — Cover the label on slabbed coins and write down your grade before revealing. Track your accuracy.
4. Join a grading group — Online forums and local coin clubs often have grading exercises.
5. Accept that grading is an opinion — Even professional graders disagree. If you're within one grade point consistently, you're doing well.

Up Next

The final article in this series: Free Resources and Apps for Learning to Grade.