There are a number of small, inadvertent actions that can end up costing you big. These mistakes range from errors of omission, such as not inserting the proper cushion packing when wrapping a valuable coin for transit, to errors of commission, such as removing an adhesive sticker from a coin holder.

So I put together a short list of some of the most common small, inadvertent actions that can end up costing you big.

Dropping a pure gold bullion coin. Gold bullion coins that are 0.9999 fine, such as Canadian Maple Leaf and American Buffalo one-ounce gold coins, are by nature very soft. These coins are not made with metals such as nickel that would serve as hardeners. If you accidentally drop one of these “soft gold” coins on a hard floor, it might dent the edge. That damage could cost you $35 or more in decreased value. These coins are so soft that even storing Canadian Maple Leaf gold coins in rolls can cause surface damage and tiny edge dings. One prominent dealer told me that a roll of 0.9999 fine gold bullion coins he bought from another dealer had to be discounted by $8 per coin because the coins touched each other in transit, with friction visible on the surfaces.

The moral of these stories is to view coins over soft surfaces and carpet your safe. Don’t store soft gold coins in rolls—always use individual non-polyvinyl chloride (PVC) plastic flips.

Tossing out a display box or removing coins from original packaging. The tendencyto be neat and compact often comes with the territory when storing large numbers of valuable coins in what seems like unneeded bulky display and storage boxes. You might want to recycle your old Amazon boxes but be very careful about throwing away the original boxes that accompany proof gold coins. For example, proof gold Chinese Panda boxes from the 1980s and 1990s sometimes command hundreds of dollars per empty box. In fact, an entire aftermarket has developed just for coin storage boxes. Even proof US American Eagle boxes can be worth $10 or $15 each.

And be very careful about removing US and world coin proof and Mint sets from their soft plastic packaging. Aside from damaging the coins, you could drive down the premium value by 50% or more.

Dropping a coin in its protective plastic holder. Certification services NGC (Numismatic Guaranty Corporation) and PCGS (Professional Coin Grading Service) may have solved the grading, authentication and storage debacles for millions of coins by encapsulating them after authentication and grading in sonically-sealed, tamper-evident holders. But if you drop one of these coins in its protective holder, the holder sometimes cracks or chips. This might protect the coin from damage, but the holders themselves have become valuable in their own right.

eBay buyers demand undamaged and completely intact NGC and PCGS plastic holders. Small cracks or chips can discount coins by $15 or more, as the cost of reholdering the coin needs to be covered. And full disclosure about the broken holder needs to be made before sale.

One little-discussed area of holder damage involves the shipment of bulk certified coins. The US Postal Service, as well as private couriers, do not always gently carry boxes of coins. Always include adequate cushioning or protection between holders so that the coin holders do not touch and are not stacked for shipping.

Losing a certificate that accompanies a coin. In line with my advice about keeping original collectible coin packaging intact, accompanying certificates and documentation should be retained, too.

In the years 1972 through 1974, the US General Services Administration (GSA) sold its hoard of about 2.9 million Morgan silver dollars that were made at the Carson City Mint. Accompanying each Carson City dollar in its display box was a serially numbered certificate. Today, those certificates have value. A certificate printed to accompany the Morgan dollar dated 1879 from Carson City is worth $350 or more. Write on the little card with a ballpoint pen, and the card will lose $200 or more of its value. Cards for the Morgan silver dollars dated 1890 and 1891 from Carson City carry values of $150 apiece or more.

Throwing away a shipping box or misplacing a coin. Before throwing away any shipping box, rip the box apart, and check it for hidden coins. Sometimes a small gold coin not even intended to be included in a shipment is hidden under a flap. Other times, the coin or coins you are expecting are somewhere within a difficult to see area of the box. Many dealers hold incoming boxes until all coins are accounted for and beyond.

Misplacing a coin is an altogether different matter. Some dealers and collectors have been known to put their more valuable coins in a “safer” place than their less valuable coins—and then forget where that safer place is. My recommendation is to always include the storage location —safe, safety deposit box, safe room, etc.—of each coin with your coin valuation spreadsheets.

Shining up a coin holder and removing stickers. The plastic slabs of certification services NGC and PCGS facilitate sight-unseen trading of coins and promote a universally understood grading system. But as I wrote earlier, the holders have become sought-after in their own right.

Coins in the older holders of NGC and PCGS often carry premiums for a multitude of reasons. And if you damage one of these older holders and need to get the coin reholdered, the grading service will place it into a new holder.

A number of things can damage grading service holders. Using harsh cleaning chemicals on the plastic will cause a cloudiness and make the coin difficult to see. Even removing an adhesive price sticker, if not done carefully, could damage the fragile tamper-evident hologram embedded on the back of the plastic holder. And some coin buyers insist that their certified coins should sport only completely intact holograms. If in doubt, ask your dealer to remove the adhesive price tag, or leave it alone. One of my greatest skills, up there with coin authentication, grading and pricing, is removing adhesive price tags from the backs of coin holders without damaging the holograms.

But the most valuable stickers of all are those issued by CAC (Certified Acceptance Corporation), which verifies with oval green holographic stickers on the front of grading service holders that already-certified coins are high-end or solid for their grades. Remove one of these stickers inadvertently, and a coin in a grading service holder might plummet in value, unless a knowledgeable buyer recognizes the coin for being solidly graded or high-end for its grade. Some CAC coins have been known to sell for double the price of their non-CAC counterparts. Removing one of these stickers might be reversible for a nominal fee. CAC keeps track of each coin it verifies and after re-examination might re-apply its coveted sticker.