People's core values will have a huge impact on their ethical behavior. This is because their core values will serve as the basis of their actions. Their core values will tell them what goals are important to them and how important various goals are.
For example, if a person's core value holds that the most important thing is to provide a good life for his or her family, that person will act in ways that are aimed at this goal. The person may act in ways that will harm others (for example, by cheating clients) so long as that allows them to make money and provide for their family.
Alternatively, a person whose core values are centered more around social justice will act in the opposite way. This person may well give up opportunities to make money or to advance if they think that those opportunities would force them to do something they think is wrong. They might, for example, refuse to take a lucrative job with a company that they think abuses the rights of workers in foreign countries.
In this way, core values provide people with a foundation. These core values tell them what is important. Once they know what is important to them, they have guidance in how to act in various ethical dilemmas.