Very recently action was taken against someone, I won't name names as it's not appropriate to discuss action taken on others unless they make it public, but before doing so it was discussed at length with one of the community devs, and while it's not really something we wanted to do, it was agreed a ban was necessary. Just because you get a PM/Warning from X moderator, it doesn't mean that it was them who spotted the infraction. If something is discussed in private, often times it is the next moderator on scene that deals with it. Like wise there are times where we spot something but don't have time to act, so you ask a fellow moderator to deal with it. I'm around a lot, it's statistically more likely during European daylight hours that I am the one to be active, so naturally I appear to be doing more. I'm also currently out of work, so yeah I have way too much free time to moderate.
Did it occur to anyone there's nothing we can do in this case either? Clearly not.
When I see a post that breaks the rules I deal with it.
Then I will then check the moderators forum & moderator logs for mentions of the username to see how often they break the same rule. If the same (or even multiple rules) are broken frequently I will see how many are from the last 4 weeks, then depending on the severity of the infraction I will issue a warning or PM using 3-strike (serious stuffs) or 10-strike (minor stuffs). Some times something is severe enough to warrant immediate user action, but that is thankfully rare. Rule section  would fall under serious stuff.
That's how I deal with all infractions.
Take into account all moderators/admin can see action taken against any individual, even the stuff we don't discuss in private is still automatically logged by the forum. If other moderators disagrees with an action it can be undone/discussed. I know at least one moderator who checks the logs daily (he may need help).
Bias is often called when people get moderated, I've seen it for years over multiple different forums both as a user and moderator. At the end of the day, people don't like to accept their faults, so if blaming others or saying it's bias makes it easier for them to deal with than accepting they broke the rules and got called on it, then that is what people will do.
@yiannis "In my opinion you should be able to register in the forum with your steam account or any other means of evidence you bought the game(s) legally.."
I've asked for this too. It would solve so many issues and cut down on abusive members with multiple accounts.