a) the bounty / airdrop / giveaway / whatever doesn't require them.
b) the bounty / airdrop / giveaway / whatever is breaking the rules.
c) the user is already prohibited from participating on the forum (e.g. his other account got banned)
I've updated the stickied thread to clarify what I mean by "not required" or "not allowed"
What if they have not stated they require the posts on their thread but are requiring it on their discord? Are you looking that into depth or should be stated on their bounty thread that these proof of authentication posts are required? I would like to help reporting stuff in the bounty sub forum but have never really understood the specifics of authentication posts.
Stating it in outside sources is fine as well (though there could be some edge cases I haven't considered). I'd limit the reporting to cases where the giveaway breaks the forum's rules or the OP explicitly stated that he doesn't require users to post PoA posts. If you're 100% (or at least like 99%) sure that there is no requirement to post PoA posts (a quick Google / DuckDuckGo / Startpage search will usually reveal something if there is one), go ahead and report them.