Keep an eye out of this platforms that offers bitcoin exchange source code especially if you do not have a deep background or extensive technical knowledge on this matter since building a cryptocurrency exchange is not as simple as we might think.
Building an exchange should be done deliberately and having the control of people's money, and being the intermediary of their trades needs a well-educated technical team behind a complex project. Secondly, it is a no-brainer that opening an exchange also needs to consider the legal implications as it will serve as the protection for people who uses the platform especially if the source code you will be using is not originally created by you.
In fact, people with no programming background should not use an open source code of a bitcoin exchange because of the possibility that it might have a backdoor written on it which can cause a catastrophic failure of funds being lost.
Investing in a bitcoin exchange should be studied first before you do some actions regarding this.
In making an exchange, you need to have a huge budget because it is not a cheap investment than you think. There are a lot of things to consider before you do it, the market, the people, the prices, and etc.
But if you really want to create one, you should hire someone that is knowledgeable about programming, the market, or people who are professional when it comes to this platforms. And that will be included to your expenses, earning reputation is easy once you are giving good service to your customers but still you need to take care of their money because that's your priority to prevent bad reputation.