Tell me my understanding that buying the underlying assets is used to deliver forward contracts. When they opened the warehouse, the basis was locked. If the capital cost, transaction cost and spot storage cost are not considered (the reality is to consider these), then the transaction is risk-free.

For example, I now buy corn at the price of 2000, store it, and sell the futures contract at the same time, assuming the premium state, 2200 yuan. Earn 200 when delivering the goods.

This is a strange way of asking questions. Level should not matter. What matters is whether the basis is locked in this transaction, which is the source of profit.

If the delivery price is higher than the forward price, the arbitrageur can obtain risk-free profit by buying the spot of the underlying asset, selling the forward and waiting for delivery, thus pushing the spot price up and the delivery price down until the arbitrage opportunity disappears.

If the delivery price is lower than the forward price, the arbitrageur can make a risk-free profit by short selling the spot of the underlying asset and buying the forward price, thus causing the spot price to fall and the delivery price to rise until the arbitrage opportunity disappears.