How can I decline the request to help a fellow student cheat? I have been helping a fellow student through a class I'm taking this semester - sending him homeworks, helping prepare him for tests, etc. The other day we had our final, which was online, and he asked me if he could pay me to send him the solutions after I turned in my test. (The program immediately gives you the answers when you finish.)

Somehow at the university I go to this is complete commonplace; people are consistently cheating on every test, every assignment, it's totally normal for me to be asked by a classmate I don't even know to help them cheat. Maybe it's something about me that broadcasts to people they aren't at risk of me snitching. I have recently decided I no longer wanted to participate in this, but I have had trouble telling people politely that I won't be helping them.

I have no desire to bring this up to any administration, because it's not a big enough deal to me, but it is a big enough deal that I don't want to be included. I also don't have any desire to moralize to these people, because first of all what do they care, and second of all what do I know. But I do need some help navigating this extreme culture of cheating. Thanks.

Edit: It is clear from the responses that I missed some important context. I have no problem with saying no to people I don't know and don't like, but I am coming from a position of formerly participating in this cheating. Thus it will be easy to misinterpret as self-righteous. "No, and leave me alone" is insufficient because it leaves my acquaintances wondering what changed. Not that I overly care whether they understand my decision, but I don't want them thinking I basically cheat when I need a grade and judge others for doing the same.
‘‘No’’ is a complete sentence.