I feel that it creates conflict of interest.  

In my opinion to be a great mentor/ strategic guide you need to be IMPARTIAL. As soon as you have active business interests with that client there is a real danger of that water becoming muddied. I’ve seen it happen in other mentor/mentee relationships, and it saddens me.  

Who agrees / disagrees with me?

In the mood for more strategic thinking?

There's plenty more where that came from...