Hello, I want to buy bitcoin, how can I be sure that they were not used for any shady business? If I buy directly from a person, what is the chance that I will have problems later? Do I only have to buy from exchanges?
Please, forgive my ignorance.
There are no stupid questions, only stupid answers

so let me help here.
You can't be sure, same as you can't be sure that dollars you get as paycheck were not used for any shady business.
I heard about some studies that most (!) dollar bills got traces of cocaine on them.