I am quite sure that when it comes to offering business advise to someone, a person must be an expert himself. The fact of the matter remains that offering bad advice may also damage the relationship between you and others, especially if you are working as a professional financial adviser.
When you give a bad business idea that is not feasible, it's most likely going to be found out by the person whom you gave such advice. As long as the person can add a little bit of common sense in the evaluation of whatever advice was given to him or her, they will know it's for their business ruin.