The OP would not owe sales tax. The OP would not be credit card factoring. The OP would have to worry about his bank filing SARS.
But I WOULD REALLY WANT TO KNOW WHY MY FRIEND HAS SO MUCH CASH AND WHERE IT CAME FROM.
The OPs friend could be getting cash from blood diamonds, drugs, arms dealer, or Super Fake Notes (which are fake bills printed by people who hate our country AND CAN NOT BE DETECTED AS FAKE) etc.
I would be more concerned with moral issues than legal and not just accept some story of where my friends money came from and that is was clean money.