It really depends on the product, seller and volumes.
I generally go by % rather than a price offset as a rule.
(Back in the 2000s I developed and assisted in a couple bullion dealer sites with buy and sell margins based off live pricing where a % and an offset were designated for specific products and weights for coins and bars etc.)
My suggestion there was to actually leverage a "better price of" the current live spot, hourly moving average or daily moving average. Depending on the quantity of products available...
I.e... to buffer a buyer/seller (trader/dealers) available stock for facilitating trades, etc. Where hedging could be placed to account for risks to stock levels.
Take your current online sellers.. are their prices for coins and bars premiums as a % or $ value going to change as the price goes up?
If they hedge on paper... but run out of stock?...
Sure... but their buy amd sell spread is going to have to match that of their customer bases average ranges.. and as their suppliers: i.e: perth mint or other manufacturers prices also vairy...
So i see perth mint kooks going at perth mint itself for $61 right now..
As price goes up.. take that is a $10 premium or a 20% premium. And their stock level is set to "backorder"... then if prices rise and those backorders pile up... their will come a time the dealers will be buying from the public to fullfill orders for metal, to fufill sales Back to the public. Their buy spred may have to go up, or their range will become (whatever the market offers) or their sell price (premium) will have to go up.
If that doesnt keep up with paper prices and disconnects occur then you may find that certain market segments make BIG profits buying at spot and selling at big premiums IF:
Sellers on market places also sell.. at spot.. while general availability... drops.
I might list.. say.. 1000 oz of genetic PM bars here in the future at 50% above spot...
As available.
Feel free not to buy it unless cant find a better deal and want the volume...
Alternatively i might place an offer to buy 200oz of "scrap lunar series 1 coins at spot-5%"
It people are looking to buy or sell here, vs a dealer who can offer spot or better for "coins" then thats fine.
Theirs a level of resale expectation that i would even consider buying 1000oz of scrap for (and hedging that purchace just to OWN the metal now, to sell at a premium when the price drops...) it would be based on a % change.. not a $offset however.
For some items, if their is availability at bullion dealers and the perth mint, and prices go up (i.e.paper traders push it around without actual investor silver moving to industry or strong hands) premiums can drop as people take a profit on their buys...
But if its a consumption driven price increase, then the people that are selling low premium may have other reasons for a quick sale.
Imo. Current prices reflect war comcerns, russias 500Mill ruble annual increase in strategic silver aquisition. (Thats relatively large..considering they also mine it.)
And samsung silver battery tech that may power future EV in rerplacement for lithium as a futre use case... not to mention current election upcoming.
I dont think russia will be using it for battery manufacturing... but they do also have platinum and palladium and may be able to do some magic if they focus on a hybrid hydrogen tech... if they dont "blow" it.