Take paper gold as an example. The difference between buying and selling is the spread. Generally speaking, banks earn profits through spreads. If the spread is 0.8 points and you buy at 300, then the buying price is 300.8 and the selling price is 300. This 0.8 is the price difference, which is why buying and selling are different. The same is true for spot gold, except that there is a little difference between the buying price and the selling price.
The buying and selling price of physical gold is different from that of electronic disk. Electronic disk can be said to charge no fees except the price difference, while physical gold has processing fees, tax costs and profits, so the price difference will be relatively large. For example, the price of gold in the bank is one gram in 280 yuan, and when you buy it, you buy one kilogram of gold in 280 yuan. When you sell it back to the bank, he will charge a spread.