The commonest complaint about the economy in Graveyard Keeper 2 is that nothing you make seems to be worth what the tooltip says, and that the shop cannot afford it anyway.
Both halves are true and both have a way round them. The price is a valuation rather than an offer, and a shop’s purse limits the coins it hands over rather than the size of the deal.
The tooltip price is a valuation, not an offer
Two hundred and fifty three items have a buyer somewhere in the game, and they split into two groups. Fifty two pay their listed price flat, and those are the tools, weapons, fish, bags and certificates. An 
Iron Shovel fetches its whole 1,750 and a 
Steel Sword its whole 25,000.
The other two hundred and one go through a curve. A sale pays three quarters of the listed price at best, adjusted by how many of the thing the shop is already holding, and it never pays more than the listing.
Every shop opens with its shelf full, which discounts you
A vendor is handed his complete shelf count the moment he opens and again every time he upgrades. So the counter you walk up to is already stocked with the thing you came to sell, and the curve reads your sale against his pile rather than against an empty shelf.
The jeweler opens holding ten 
Fine Jewelry, so the first one you sell is priced against eleven and pays 35,755. The same arithmetic takes a 
Golden ingot from 10,000 to 6,847 and a 
Philosopher Stone from 5,000 to 3,575.
Precious Trinkets lists at 10,500 and the Trademaster, who has the deepest purse in town, pays 7,509 for the first one.
Nothing you do empties that shelf cheaply, because buying his stock back costs the full listed price rather than three quarters of it. Treat the discounted figure as the real number and the tooltip as an upper bound.
If it is not on his tier list, nobody will buy it at all
A shop can only trade what its current tier lists. An item that appears on no list anywhere cannot be sold to anyone at any price, and an item that appears only on a later tier is unsellable until you pay for the upgrade.
That is 132 of the 253 available at the counters as you first meet them. The other 121 are waiting behind a merchant upgrade, which is why an expensive thing can look worthless for most of a playthrough.
Some never get a counter. 
Imported Components is valued at twenty thousand, a 
Steel Ingot at a thousand, and the four trophy fish from the 
Elder Catfish to the 
Kraken Jr run from three thousand upward, and no shop in the game lists any of them.
Fine Jewelry appears twice on his third tier list and the first of the two entries carries a shelf count of zero. The lookup takes the first match, a shelf of zero prices the item at nothing, and the floor in the pricing code turns that into one coin.
Sell every piece you own before you raise him past his second tier, because the offer does not come back.
The purse is not the wall it looks like
A deal is checked once, on the difference between the two sides. The game adds up what you are selling, subtracts what you are buying in the same window, and tests only that number against your coins and against his.
So a shop holding twenty coins can complete a thirty five thousand coin sale, as long as you take thirty five thousand back in his stock. Fill the buy pane with his flasks, ingots, seeds and potions until the total at the bottom drops inside his purse, and the trade goes through.
Most things worth more than a thousand coins are worth more than the shop that buys them is holding. Without the net rule almost none of them could ever be sold, which is the wall most players hit and read as a bug.
It also runs the other way. You can buy something costing far more than your purse by putting enough of your own goods on the other side of the same window.
What comes back is goods rather than coins
What the trick does is convert value. You walk out with his shelf rather than his purse, so the honest way to read it is as a way of turning things you cannot use into things you can.
Two limits bite in practice. Your backpack has to hold everything you take back, and he has to be stocked with enough that you want, which is why a shop at its first tier is a poor place to unload something huge.
For coins in hand, the town still only spends what it has. That is what a sermon is for, and where the real money in a save comes from.
Graveyard Keeper 2 trading FAQ
Why will nobody buy my expensive item?
Either no shop lists it at any tier, or the shop that does has not been upgraded to the tier it appears on. Only 132 of the 253 sellable items have a buyer at the tiers you start with.
Why do I get less than the price on the tooltip?
A sale pays three quarters of the listed price, adjusted down by how many the shop already holds, and every shop opens with its shelf full. Fine Jewelry lists at 50,000 and the first one fetches 35,755.
How do you sell something worth more than the shop has?
Buy from the same shop in the same window. Only the difference between the two sides is checked, so a twenty coin purse can settle a thirty five thousand coin sale if you take the rest back in goods.
Which items pay their full listed price?
Fifty two of them, and they are the tools, weapons, fish, bags and certificates. An Iron Shovel is 1,750 and a Steel Sword is 25,000 with no shelf discount at all.
Should I upgrade the jeweler?
Not until you have sold every piece of Fine Jewelry you own. His third tier lists the item twice and the entry the game reads has a shelf count of zero, which drops a 50,000 coin sale to one coin.
What is the fastest way to make money then?
Sermons. No vendor is involved so no purse applies, and Prayer for Old God pays fifty coins a head to a congregation of a hundred and eighty.
