“the dealership has the burden of verifying the spot price of gold or silver”
I doubt many businesses will want the hassle of dealing with a volatile form of payment.
Gold was $3,300 when the customer bought their merchandise last week - now it’s $3,200 - now it’s $3,150 - oops!
Of course, it can go the other way, in favor of the business. But how many businesses will want to take the chance? Probably none, other than the Mom and Pop kind.
The value of the U.S. dollar, objectively measured, also varies.
You might want to consider cutting precious metal coinage a little slack.
It will depend on how much they want the sale and what tools arise to make it easy to instantly evaluate purity and weight.