How to know if a woman is a cheater?

I didn't want to make this post but a friend of mine just lost his girlfriend to a bull and im getting bit frustrated with women. Yesterday my friend, he just broke up for a day, he was visiting a new apartment, he wanted to move out of this one since it was just him now. Anyway his sister is a mid 20 and a mid is the female version of a low effort invoker. I once asked her students what she teaches them and she said well she students don't even learn, most just go for the 3rd year mid course so they could qualify for a government job. Since she enjoys sending students to become teachers, most just go for teachers courses not because they want to teach but because of the 3 year system. Anyway back to my friend, he got angry about his non existant ex and said he's not gonna fall in love anymore cause it's rigged. Then the invoker sister said "yeah most women are cheaters it's not just your girlfriend that cheated most of my friends are cheating on their boyfriends". I just stared at her when she said this and I was also surprised that the mid enjoys telling students to lie in order to get government jobs. I also remember her sister (i.e my friends ex) when she took out her iphone 13 to take selfies, she paid 900AUD for that new phone, it was considered brand new because she bought it in 2021. I remember being shocked at that price, all of my phones are chinese brands anyways. But back to the topic, how to know if a woman is a cheater or not?