We recently won an online auction for 20 "Engelhard" prospector silver rounds at just about spot price, $30 each. The seller had 2 feedback, probably explaining why the auction closed so low. Each round came in its own plastic airtight capsule, and each was gleaming white. We were suspicious. After all, these rounds are dated 1984, and even in an airtight silver usually tarnishes.
The rounds weighed between 30.5 and 30.9 grams each. That's also a problem. A troy ounce is 31.14 grams. Sure, 30.9 is pretty close, but we weighed a bunch of other silver rounds and bars we have, including an Engelhard ounce bar. All weighed at least 31 grams, usually more, like 31.1 - 31.4. This made us more suspicious.
We took a screwdriver and a hammer and went to work on one of the 20 rounds, to see if we would find a smoking gun under a thin coating of silver. Unfortunately that was inconclusive; it still looked silver.
Finally we took these all to a local coin shop. They weighed them and said they could be real. I let them file into the one I already attacked with the screwdriver. They applied the acid test. Then they concluded these were totally fake! It was satisfying to have an answer.
The seller on the auction site had requested I leave positive feedback immediately after I received the rounds. That is a little suspicious too. If you use the most well-known auction site, you are usually protected against loss to fraudulent sales, like this one. But not if you leave the seller positive feedback before you discover the fraud. We have also seen fake gold coins from popular auction sites, but those too were far underweight, so easy to detect. So don't be rushed into leaving positive feedback before you have satisfied yourself that what you received is really what you paid for.
At the coin shop, the dealers, who looked to be in their 70's, said they had seen more and more good fake coins. They believe these fakes come from China. Usually, they said, the weight was too far off to be hard to detect. But now, like these Engelhard 1984 Prospector rounds, the weight is very close so it is not easy to tell.
Be careful out there. These are not just on popular auction sites. They can be in your local coin shop, from the popular online metals exchanges, anywhere a buyer isn't careful enough to inspect their goods on arrival. Don't be the dope.