How do u handle things when you know you are being scammed?

Need some help here. I received an IM 3 days ago from a guy who said he lives in CA but is in Nigeria on business and that he had a 12 year old boy. Then, this nut asks me to marry him. I told him I didn't even know him. Then, he writes me this extremely long love letter. Yeah, really a bunch of BS. Haven't heard back from him. Thank God. Then, I get 2 more IM's. Both guys had the same story as the first. A widower with a 12 year old child, looking for someone to love. Guess what? These two guys come from Nigeria also. I asked for profiles and only two showed me theirs, which were sketchy at best. It didn't look like yahoo personals profiles. The pictures of these guys where white males, very professional looking. Too good to be true. They had suits and were clean cut. And everyone is from Nigeria. They//whoever always gives me the same line of bull then I put them on ignore. Does anybody else get IMs from these nuts? I never hear back from the guys I want to meet. Getting discouraged