Blacklist all the one that made a GA of a free game! (lvl 1+)

No, specifically, a minority may not know because they're giving away copies of games they had sitting around in bundles and so forth.
While the majority are bound to be in violation of the rules, it's always a bad idea to make assumptions on such matters, since there's always the probability that someone simply had bad timing.
After all, how often do you yourself check ongoing giveaways for games you're planning on giving away, before making those giveaways?

I'm not going to knock getting upset over regifting, since that's one of those mind-boggling things that just intuitively seems wrong to begin with, at least to the point of compelling you to look into the rules before going down that route [that said, everyone has moments of carelessness, so some grace in the response is called for].

But as far as free giveaways go, they don't hurt anyone [yes, it's distasteful and entitled to grab free games you don't plan to use, and it's never praiseworthy to engage in exploits, but as an immediate outcome, everyone ends up getting bonus P from the giveaways- so if anything, you can view it as a positive, if you assume that all free giveaways will get deleted in time (though, in fairness, I've encountered many instances where they remained in account indefinitely :/ )], and unless you spot a pattern in the user's giveaway history, there's no justification for assuming the person actually violated any rules, even if the odds are highly in favor of that.