1. U.S. Securities and Exchange Commission (SEC). (2013, January). Investor Bulletin: Closed-End Funds. SEC Publication. On page 1, it states, "An investor wishing to sell closed-end fund shares must sell them to another investor in the secondary market... Like stocks, closed-end fund shares trade on exchanges... When you buy or sell shares of a closed-end fund, you may pay a brokerage commission to your broker."
2. Financial Industry Regulatory Authority (FINRA). (n.d.). Fund Facts: An Introduction to Closed-End Funds. In the section "How Closed-End Funds Work," it clarifies, "Unlike open-end mutual funds, closed-end funds are not 'redeemable,' meaning that investors who want to sell their shares cannot sell them back to the fund. Instead, they must sell their shares to other investors on the secondary market... When you buy or sell shares of a closed-end fund, you will pay a brokerage commission to your broker."
3. Bodie, Z., Kane, A., & Marcus, A. J. (2018). Investments (11th ed.). McGraw-Hill Education. In Chapter 4, "Mutual Funds and Other Investment Companies," Section 4.2 discusses that closed-end funds "are traded on organized exchanges and can be purchased through brokers just like other common stock; their prices, therefore, can differ from NAV." This confirms the trading mechanism involves brokers (and thus commissions) and market prices (bid/ask).