It always makes me sad whenever I see almost-obvious alt accounts on "congratulations to the winners" section of contest announcement posts, especially in Div. 2 contests where there are no trusted participant rules. Of course, maybe some of the "grey participants" are actual honest accounts, and in that case I really want to congratulate them. But due to how many of them are likely to be alts, I already start hating most of the mentioned handles.
I think the most effective way to prevent alts is to eliminate motivations to create alts in the first place, and winning lower divisions could be one of those high motivations. Well, there could be not many who can actually try to win them, but due to these alts, people who actually deserve high places can't even get there at all.
It's sad that they can't be praised enough if we stop mentioning the winners, but I'd want to give them a more deserved place in the standings table (this also helps many many top 100 participants), rather than seeing alts being praised by the official announcement and be biased to think that all the winners could be alts.