trading rules

If you are a broker, you earn commission, not the price difference between the seller and buyer. You sign contract with the side from which you will get paid. If you represent seller, you takes a % of total sales, which is in most case. But sometimes the buyer pays commission too if they try to buy something hard to find. Then you need to sign contract with them too. But the final price is known and agreed by both seller and buyer,you are not going to hide any information.

If you want to earn the price difference between two, then your company needs to become the buyer and seller yourself and advance money and take the risk of not being able to find a buyer or seller later. In that case , show your 銀行信用證明 is enough.