American dealers stock platinum coins, yet buying and selling one is a noticeably different experience from doing the same with gold. The metal is not the problem; the size of the market is.
Retail demand is a fraction of gold's
Platinum's use is dominated by industry, especially automotive and chemical applications. Investment and jewelry demand together make up a much smaller share of consumption than they do for gold.
That means far fewer coins are struck, far fewer buyers ask for them and far fewer dealers keep them in stock as a matter of course.
Thin retail participation is self-reinforcing, since the products stay unfamiliar to the buyers who might otherwise create the demand.
Fabrication runs are small and irregular
Mints produce platinum bullion coins in limited quantities, sometimes with substantial variation from year to year depending on expected demand.
Small production runs carry higher cost per ounce, because setup, quality control and packaging are spread over fewer pieces.
That fabrication cost appears in the purchase premium, which typically sits above the equivalent premium on a comparable gold coin.
Dealers hedge platinum less comfortably
Hedging inventory requires a liquid futures market. Platinum futures trade in far smaller volume than gold futures, so laying off a position is harder and can move the price.
A dealer facing that difficulty protects itself by widening the quoted spread rather than by refusing to deal.
The wider spread you see at the counter is therefore an accurate reflection of the wholesale market behind it.
Resale depends on finding an interested buyer
Selling a common gold coin is close to automatic, since any dealer will bid. Selling platinum can require contacting several, and bids may vary more widely.
Some shops will buy platinum only at a substantial discount, because they have no ready onward buyer and must ship it to a refiner.
The metal retains its value; the friction of converting it back to cash is simply higher than gold's.
Price behavior differs from gold's as well
Because industrial use dominates, platinum's price responds to manufacturing conditions and vehicle production in a way gold's largely does not.
Holders sometimes expect platinum to behave as a substitute for gold and find that it tracks industrial cycles instead.
Understanding which demand base sets the price is the difference between reading platinum accurately and reading it as a rarer version of gold.