The buying price of cash refers to the foreign exchange transaction price when foreign exchange cash is converted into RMB. That is, the price you sell to the bank.

Selling price refers to the foreign exchange transaction price executed when buying foreign exchange with RMB. That is, the price that the bank sells to you.

Buying and selling are all from the perspective of banks. For example, if you change foreign exchange into RMB, then the bank is equivalent to buying foreign exchange in RMB, so the purchase price is implemented. Different banks have different exchange rates. China People's Bank is higher. The exchange rate is variable.