I too have been asked many time to trade friend's money - never did. The extra burden is not worth the risk. If I'm good, I rather profit from my money, because the "trader manager fee" isn't worth it.
That's right, no matter how good you are in calculating profit and loss, it will still be a burden on your own for your trade and if your friend wants to get a profit in trading, then it's enough to give your input and other suggestions so they also have the courage to trade in its own way.