I didnt know that bid bots can effect the reputation and it is true, I find it also weird to flag someone with high reputation. I also noticed many users selling and buying accounts. That means anyone with high reputation can sell the account to a spammer.
There are small gangs upvoting each other. A group of 3 or 4 accounts upvoting their spam comments all the day.
Personally I check the comments of the accounts that I dont trust to make sure if they are spammers or not. It became very complicated lately. Selling accounts, phishing, spamming and Plagiarism, but they will be filtered with the time :)