so I invite all of you to do the same by double-checking the bounty spreadsheet that you are following and if you find your social media profiles on other bitcointalk accounts to give negative trust
Common accounts who are using other peoples social media profiles are those newbies. Even if they will be given a negative trust, they can just create another account and participate over and over again. The best practice is to increase your requirements in ranks and have more strict rules. This way, newly created accounts will not be able to participate and you can at least decrease the possible participants of your campaign.
You are right, there must be stricter rules for new forum members to join the bounty campaign. but giving such a negative trust to such cheaters would limit their numbers as well. the steps taken by the OP are good, just add the next step to prevent fraudulent people from joining new accounts again in the next new campaign.