Rare, unusual or valuable coins can come your way from all kinds of sources, from the heirloom bequeathed by a favorite uncle to the total surprise hiding in the attic. But until you know how to sell that treasure for whatever it's truly worth, it's a little early to start planning for a life of luxury. Here are three critical factors you need to understand if you hope to fetch the right price for your coin.

1. The Melt Value

The first thing you need to know is the absolute least amount of money you should accept for your coin. This number is called the melt value, and it corresponds to the scrap value of the raw material. Even if your coin is worth nothing to collectors or historians, its metal should fetch a price tied to the ever-fluctuating marketplace. Of course this means you'll need to know exactly what percentages of various metals make up your coin. Resources such as the USA Coin Book break down these percentages for specific collector's items and even tell you the exact melt values of the coins in question.

If you have a "mystery coin" with no published melt value, you'll have to estimate the amount of precious metal in it yourself. A local jeweler can perform various tests to check the purity or karat value of a gold coin, for instance. Once you know the percentage of precious metal in the coin, you can use online calculators to determine its melt value.

2. The Red Book Value

Your coin could be of tremendous value no matter what's it's made of. Dedicated collectors can pay enormous sums for an exceptionally rare or culturally significant artifact—but if you're not a collector yourself, you may have no idea how enormous that sum ought to be. Fortunately, professional reference guides contain comprehensive lists and descriptions of different coins and their retail value based on their condition. One of the most highly respected and widely used sources is the Red Book, more properly known as the Guide Book of United States Coins. This book is revised and updated constantly to keep up with changing values, so make sure you purchase the most recent edition available.

3. Where to Find (Qualified) Coin Buyers

Once you have an accurate picture of what your coin is worth, you can sell with confidence—but to whom? Coin buyers can be found in a variety of environments, from scrap metal merchants who buy gold (if you're selling your coin for its melt value) to pawn brokers looking to resell coins to collectors. If you know you have something of significant value and you want to get a fair price for it, focus on coin buyers with verifiable experience, knowledge and ethical standards. Selling through a dealer can help you make an intelligent transaction. One of the best ways to identify a reputable dealer is by consulting the Professional Numismatists' Guild. You can also surround yourself with knowledgeable collectors by attending local or regional coin shows.

The sheer ease and convenience of online selling platforms such as eBay can be very tempting, and it is indeed possible that an expert collector will spot your coin and offer approximately what it's worth. At the same time, however, there are many more rank amateurs and bargain hunters who may keep the bid price ludicrously low because they simply don't know the value of the coin. In this situation, it's better not to accept bids at all, instead setting a fixed price based firmly on your coin's listed Red Book value.

Keep these considerations in mind and you can rest assured that you're getting best price for that special piece of currency. Whether you strike it rich or just pocket a few extra dollars, you'll be glad you sold your coin the smart way!