Unsold marketplace prices are not comparables. Exact completed sales and matched attribution matter.
The practical lesson
Start with the complete coin and a neutral description. Record weight, diameter, edge, both faces, lighting, and the proposed production mechanism. Then compare damage and ordinary varieties before assigning rarity.
Build a defensible comparable-sales record
For each alleged rarity, save at least three pieces of evidence: a clear attribution for the exact die variety or mint error, grade and surface-condition details, and a realized sale with date and fees. An unsold $50,000 listing provides no proof that a buyer paid that amount. Use completed auction archives and certified population records where possible; compare identical denominations, dates, mintmarks and diagnostic markers instead of grouping every “double” or “off-center” coin together.
Estimate an appropriate range from multiple comparable transactions, then account for buyer's premiums, seller fees, shipping and certification. If no genuine match exists, say the market evidence is thin rather than assigning a precise number. For doubled varieties, our doubled die reverse guide shows why attribution comes before the price discussion.
Why collectors get trapped
Error coins are visually exciting, and online marketplaces reward dramatic titles. That combination encourages conclusions before evidence. A better habit is to make the coin pass a series of disproof tests.
What to save
- Original photographs
- Scale and caliper readings
- Seller description
- Certification lookup
- Sources checked
- Exact sold comparables
Uncertainty is not failure. “Unresolved” is a better collection label than a confident but physically impossible error name.
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