>>60935082
>Downside being that if you're looking to make a big sale you're testing 1,000 coins out versus one bar.
I'd take the thousand coins because I can test them non-destructively. Trying to think where I could find a scale big enough and accurate enough to do a density test on 1000 oz of silver.

Molybdenum has a density of 10.2g/cm3 Silver has a density of 10.49g/cm3, and Mo has a very high melting point but a silver plated Mo bar could be very difficult to spot without drilling.