BU Silver Dollars With Dark Spots

If you return bullion coins, you pay at least forwarding shipping costs, and some suppliers may charge you return costs as well.
For a coin that has a value strictly based on bullion value, shipping costs are not justified.
For any bullion coin any extra costs make the original purchase cost unviable.
Such coins will still sell directly back into the bullion market for their bullion value anyway

So just keep them; you should not loose on a re sale.

For any future bullion investment, you may wish to choose a different bullion supplier.

Quite often, a stasher will buy a bullion item in pristine condition, only to find some sort of deterioration during their period of ownership. Also not a worry if you strictly buy as bullion, and re sell strictly as bullion.

Normal precautions should be taken to preserve their original blast white appearance, which may make re sale easier later on.

All sound advice above. But Bullion is a silver investment coin - not for a collector actually, but they have been bought up just for that purpose - most likely due to the relative low purchase price