Discovering a collection of unusual and rare looking coins left behind by a family member or friend can leave you wondering how to proceed. Most people want to keep at least a few of the coins as personal mementos, but selling off valuable ones is often appealing as well so that there's less pressure to try and maintain and protect those coins. Choose between selling an entire collection as a whole or picking out individual coins to sell by considering these four factors behind the decision.
First, try to find out if the collection was planned in any way, or if it just came about naturally as the original collector traveled or found interesting coins. Planned collections tend to have a much greater value because they were put together by someone following the various guides and cost publications to determine what to buy, sell, and keep. There's also a higher chance of one or more very rare coins worth selling alone. If you determine the collection was more random and personal, you may want to sell your coin collection as a whole since it is unlikely to contain any coins valuable on their own.
Age of Coins
A collection containing at least a few old coins, dating back to at least the early 1900s, is more likely to be worth splitting into groups or individual coins for sale. If you only find coins minted from 1950 onward, you'll have to get lucky and find a mistake in a design or an unusual, uncirculated coin to have any chance of making an individual sale worth the cost of listing. Even if the newer coins are rare or unusual, they haven't had as much time to become highly valued and sought after by collectors. Newer collections are better sold collectively, while individual old coins deserve their own attention.
Coin collectors who put together sets, even if they don't appear related to the casual observer, likely have more value in their collection. These sets generally fetch a higher price than the individual coins, with the exception of mint sets and other widely sold pre-assembled sets. A set that was pieced together through careful collection is likely to be worth selling on its own, while other more common sets can be sold together for a better price.
Finally, consider your own personal interest in coins and your willingness to spend extra time and effort researching individual coins. It's often a very hard to notice detail that makes a coin go from common to rare and valuable, so it's easiest to hand over a collection for a professional assessment and get an offer on the entire lot.