The root cause probably in this situation to why the victim agreed to invest money to a professional trader is that, he wants to have an assured profit from trading due to the label "professional". It is money which is on the line so you better put it in your 'hands' since that is your money in the first place that you invested. Asking for help and tips would be a good thing to do but depending on them to much would not be advisable. It is your money and that should be enough for you to take full responsibility of it and make decisions for yourself. It is like paying someone to do your project.

Know what you are engaging yourself into. Familiarize yourself about it to avoid being fooled by other people. If you are not that knowledgeable, do not rush things and take time to have an initial idea because there will always be people who will take advantage of the things you lack once they get the opportunity.