+1 Yes

View attached image.

That is correct. You can reroll if the user already owns the game, for partially owned content in a package, if the user doesn't respond for a week, if the user is currently suspended, if the user entered through a group that they were no longer a part of at the time the giveaway ended, if the user agrees to the cancellation, or if the user is deliberately hostile during the giveaway process for that giveaway.

Any personal restrictions are ignored as reroll reasons, though through clever use of forums and groups, you can usually fake the setup you want- though even then, there's little guarantee someone won't betray your expectations of them.

Meanwhile, Blacklisting people for their commentary habits in a public giveaway will reach the 1000 blacklist cap pretty quickly, especially with super low level giveways like this one, so that's not a feasible option, either. :X

Forum giveaways work a lot better in that regard, as more people are likely to comment to begin with [namely, since you can't as easily auto-join on forum giveaways, but also since forum-goers tend to be more invested in the community to begin with], and there's a much smaller pool of individuals to blacklist.

People get upset when you don't bother reading their giveaway description and do something they explicitly told you not to.
Whenever there's nothing in the description, you can do as you please, but otherwise you're spitting in the face of the GA creator and telling them their preferences and perspectives are less important than your desire to do whatever strikes your selfish fancy.

In RL, that'd be amazingly dickish, and that basic social courtesy extends similarly to online interactions. It's nothing special or estoeric- yes, some people will be similarly capricious with how they blacklist, but there's no changing your interactions to improve that, so no point in worrying about such users. For everyone else, the basic concept of 'don't be a dick, and respect others' applies just as well as in any other situation.

tl;dr version:
Don't worry about what people might do because of their own lack of proper communication and passing whimsy, just make sure your own communication is respectful and respectable, and you'll be fine.

You may want to avoid 'generic thanks', however, as that's the main concern- auto-join scripts tend to favor them, and they're surprisingly common on this site. Just make sure to add a few personal touches, and mix them up each time you comment. When in doubt, add a new random image each time.
Sometimes there's simply nothing to say- don't sweat it, it's the patterns of behavior that are the issue, not an individual generic response.

But yeah, when you get 18 pages of spammy thank you comments after you asked for none to be posted, it's a major slap to the face. (Remember, gratitude has to be sincere. Whenever you're deliberately rude, you're not being sincere, you're doing whatever you want because you want to do it. It has nothing whatsoever to do with gratitude toward the individual involved at that point- you could be saying anything there, the fact that you used a specific word (in this case, 'thanks') doesn't make it any better than if you used a polite word in a clearly hostile manner in normal speech. Your intent is conveyed quite well regardless, and it's clear that intent isn't meant to be positive.)
Likewise, it's an issue if you ask for a comment and none is made, which indicates the commenter didn't think your generosity worth any consideration.

Of course, either one is a bit ridiculous a thing to ask out of a public giveaway, given how extreme the amounts of users that enter without reading descriptions are in public giveaways.
With a blacklist cap of 1000, you end up filling up pretty fast that way. :X

Correction, you just can't reroll for a reason like that. Period. End of statement.

There are no longer custom rules allowed for any giveaway. Even when they used to allow them, it was only for private giveaways - if it was put up public, no custom rules either. So, effectively, this is a two time loser.