You're basically asking "do you check for red flags on everybody who is not raising red flags?"
In comment threads, I usually only check post history for people I am considering blocking. It makes sense to check post history if people are instigating. If that person is just starting shit everywhere then there's no reason to listen to them, but if they have a history of reasoned discussion then maybe what they say is worth considering. (I realize how ironic this is coming from somebody who has almost no comment history on a new account)
You're basically asking "do you check for red flags on everybody who is not raising red flags?"
In comment threads, I usually only check post history for people I am considering blocking. It makes sense to check post history if people are instigating. If that person is just starting shit everywhere then there's no reason to listen to them, but if they have a history of reasoned discussion then maybe what they say is worth considering. (I realize how ironic this is coming from somebody who has almost no comment history on a new account)