The selling price refers to the selling price of the bank. If you buy foreign exchange, you use the selling price. You sell foreign exchange to the bank at the purchase price (the bank buys it). So after a period of time, when the purchase price is higher than the previous selling price, the previous purchase can be arbitrage.

Cash remittance is the foreign exchange deposited in the bank by transfer, such as overseas remittance and traveler's check transfer. Cash is foreign currency cash or foreign exchange deposits deposited in banks with foreign currency cash. Generally speaking, the selling price of cash is the same as cash, and the buying price of cash is lower than cash.

In general arbitrage, spot exchange rate is often used.