Yes, funds mainly earn bid-ask spreads. It is a better operation method to sell when it goes up and buy when it goes down. However, investors are not advised to invest in daily trading funds, because the fluctuation of funds is not large, the probability of making money from short-term trading is small, the handling fee of short-term trading funds is not cost-effective, and the probability of earning income from long-term holding of general funds is high.

When trading funds, investors can set profit-taking targets. For example, investors' expected return is 30%, and when the return reaches 30%, they can sell the fund.