It's surely possible but it's not quite that easy, otherwise you'd see it daily in comments. It's similar for front page posts but harder since both users and moderators nuke spam-looking things as they are highly visible.
If you go to https://news.ycombinator.com/newest , from time to time there apears stories with 50 upvotes in 30 minutes, and perhaps a few sockpuppets/shills comments. If you do the math, they should be in the front page, but misteriously they aren't. So the conclussion is that HN has a secret feature that detect (some of) the tricks. I think I read some coment from pg or dang about voting rings, but it was a long time ago, but it has no details. The details are part of the secret sause.
Also people flag strange threads, so the detection is not only automatic. If you notice something strange, you can send an email to dang: hn@ycombinator.com
Kikawala|1 year ago
https://news.ycombinator.com/item?id=40117443
pvg|1 year ago
Arnavion|1 year ago
There is a whole family of pwdisswordfish* accounts btw. The "b" account's "about" text even has a holier-than-thou attitude about it.
gus_massa|1 year ago
Also people flag strange threads, so the detection is not only automatic. If you notice something strange, you can send an email to dang: hn@ycombinator.com
fragmede|1 year ago
tgv|1 year ago
unknown|1 year ago
[deleted]
wood_spirit|1 year ago
[deleted]
snakeyjake|1 year ago
[deleted]