Sniping Curiosity

I see quite a bit on this subreddit about sniping people's stupid auctions and I've begun to wonder something.. Why would anyone auction such high level items for such stupidly low prices? Why wouldn't they use the mail functionality?

I'm sure this is probably a stupid question but I am truly curious how everyone consistently seems to stumble upon such ludicrous deals. Have you ever been sniped? Why did you list?