Re-roll problem

However, that's usually under the premise of fair play (ie, not wanting any one person to get more than X wins off you, so that others can have better odds of winning from you), meaning that if the winner got a reroll, most such creators presumably wouldn't have reason to blacklist the user on the basis of having won something.

I rely on my memory to keep track on most games with DLCs. Plus, whenever they show up again, I hide them which also marks them due to the handy script I use (so I can recognize them within a train, for example). However, some people might forget once in a while, which is natural. You can't expect everyone to look into their library every single time, and people don't have perfect memory.
Also, a very large amount of multiple wins occur because of the same person winning identical giveaways over a short amount of time. Since popular giveaways often follow the trend of whatever given bundle or deal is popular at the moment, this can happen incredibly often. Just a few days ago, I won two copies of the same game from two different givers whose giveaways ended 1 minute after each other. Since people cannot be reasonably expected to check the site more than once per day, this is a very common occurence.
Finally, sometimes people don't always remember to leave ongoing giveaways for the same game after they win, or they would like to wait until they've actually received the game before leaving the other ones.
Lots of reasons of which I don't see any that warrants a blacklisting.
Besides, winning/entering more than once carries its own penalty because you permanently lost the points which you could've spent elsewhere, and you don't actually get the game twice (since that would break the rules and carry its own penalty).

Of course there are probably people who have sinister intentions, but you cannot gauge their intentions by the fact alone.

I currently have one "win" I assume will be re-rolled because I enterd for DLC that had a different name in my library, and I just checked the library entry rather than the DLC tab before entering (name was correct there).
So it's a little easy to brand everyone who experiences this as bot-users.

I wasn't aware of any situation in which feedback should be left as unmarked. Can you point me to a source of this and preferably some expanded rules on unmarked vs. Not Received?