The exchange may offer privileged services like high-frequency trading to larger clients like mutual funds and asset management companies (AMC), and earn money accordingly. There are provisions for regulatory fee and registration fee for different profiles of market participants, like the market maker and broker, which form other sources of income for the stock exchanges.
Arbitraging can be very lucrative especially with Asian markets (South Korea for example) where cryptocurrencies are exchanged at premium rates, but due to the high volatility of the markets and the congestion on major cryptocurrencies (Bitcoin and Ethereum) it is becoming increasingly difficult to do arbitraging because of potential incurred losses. Add to this the fact that exchanges need a certain amount of confirmations before balances are made available for trading and it makes it quite risky at least for Bitcoin and Ethereum.
As written in section Investing 3, you should never keep any valuable assets on an exchange, unless you engage in day trading. You should get an appropriate wallet to store your cryptocurrency safely. To explain the concept better, what you are storing is not the cryptocurrency itself, but your private keys, the keys that allow you to spend the cryptocurrency that is assigned to you and stored on the blockchain of the given cryptocurrency (of course each project has its own blockchain, just like each bank has its own internal banking system – to simplify heavily). Anyone who has access to your private key is in control of your cryptocurrency assets, so you must secure them. Most if not all of the wallets around have a feature called a backup phrase. It is a mnemonic sequence of words that must be written on paper and stored securely. If you lose access to your wallet, get it lost or stolen or whatever, this backup phrase should allow you to recover instantly access to your private keys and funds, after which you should immediately transfer them to a new address.
Michael R. Lewis is a retired corporate executive and entrepreneur. During his 40+ year career, Lewis created and sold ten different companies ranging from oil exploration to healthcare software. He has also been a Registered Investment Adviser with the SEC, a Principal of one of the larger management consulting firms in the country, and a Senior Vice President of the largest not-for-profit health insurer in the United States. Mike's articles on personal investments, business management, and the economy are available on several online publications. He's a father and grandfather, who also writes non-fiction and biographical pieces about growing up in the plains of West Texas - including The Storm.
This is a more advanced topic for those who want to do what is called « day trading », i.e. those who plan to buy and sell on a daily basis as their main activity. Arbitraging is the process of leveraging price differences between exchanges to make a profit, by buying cryptocurrency cheap on a given exchange and selling it for a higher price on a different exchange.

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