A "couple hundred peers" is a lot easier said than done. That being said, it does happen and you are correct that having a lot of seeders doesn't guarantee a safe download.

All of the three conditions I mentioned are neither sufficient nor necessary for a safe download, but there is a strong correlation. Unless the torrent is official (e.g. official Linux distro torrents), there is always some chance of a bad download. The chance can be low but is never zero.