The first time I remember hearing the word "Scam" used was when I was teaching school, taking a special education teacher's place while he did other work in the school building. He was less than happy with me, because I allowed the kids to take advantage of me. I hadn't been teaching for very long, and I believed anything the kids told me. I later learned to be more skeptical. This teacher told me that I was allowing the kids to scam me! He meant that I was believing what they were telling me and they were lying to me about what they were supposed to do, and I was believing them!
I think there are mainly two ways that scams take place, and maybe more, but two of them come to my mind. One is where the young man pretends to be what the young lady needs/wants, and he has no intention of being that, but he is just playing games with her. Why does he do it? Who knows? Maybe he is bored? Maybe he wants to get some advantage from her. I don't really know? He is telling her things she wants to hear, but it turns out that he is being untruthful to her.
Another way is when a young lady has a whole group of young men. Each man thinks that he is her one and only, and he is sending her money, and so are a dozen or more other young men sending her money, and each thinks that she is his one and only.
Another type scam is when a young lady makes a young man think that they are meant for each other, while she has a boyfriend with her. She gets the young man lured into marrying her and bringing her to his country. When she gets there she stays with him long enough so that she can legally petition someone from her country. Then she claims that he has abused her, or whatever other reason she can get to dump him/divorce him. Then she is legally in the country for instance, USA, and after that she brings her own boyfriend, and maybe her whole family to the USA, and she has merely used the young man who thought she loved him. How you can tell something like this is about to happen or happening I'm not sure, except to pay attention to the red flags or the warning signs you get. Other than that get to know the person well, or get acqainted with people who know that person.