You need to expand on your question. You "know" the person or entity is committing a scam or worse a con? What is your proof, where is your explanation for you question? 
Right now I am watching as another travel agent with a very good reputation is getting pulled through the mud because a blogger believes she scammed him when through her recommendation he purchased travel insurance. He did not read or understand the coverage and was denied a refund for airfare and non-refundable services when he cancelled a trip. It was not the travel agent who denied him, it was the insurance company. However, he is posting about her and the agency. Was he scammed? No, but this is his belief. 
If you know, beyond a doubt, legally a person has committed or is committing an illegal act, take it to the authorities. Let them deal with it and keep yourself out of the limelight.