I have DV'd people in the past and I was WRONG. Being professional, going through your steps to validate fraud, and being accountable for a mistake moves mountains
provided you have your proof i don't think you are wrong? the truth is that downvoting a plagiarized content is for the person to know that the community is meant for people to use their brain rather than free money zone. but you need to put or reference the page where you see the content that is the way to justify the downvoting if not one may misjudge the writer for is effort.