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.
The risk in trading always exists and that stress of trading on somebody else money just increases and better not to overburden at times. Even I think trading for our self without own money is much better atleast we are not answerable to anyone other than our self. Volatility is always there so at times you can get the trade wrong and can lead to some losses as well which is though a part of trading itself.