You must manually check the backlinks to see if they are bad or unrelated backlinks.

Unrelated links aren't a bad thing, if they are on spammy article or directory sites that only exist to build links to other sites, then they might not be good.

Focus on building quality links and not worrying about the links that already exist.

There are some tools to see which sites are linking to your sites Like Google Webmaster Tools, backlinkwatch.com, ahrefs.com, etc

You will soon see Google penalizing your competitor. It is not always good to do what your competitor does. Using our brain sometimes can help us from suffering.

If you didn't find it before google then it could be penalized. So it's better that always check website pr and quality on which you're going to promote a website.

You can check all the backlinks where you pointed your website but you can't actual spammy links. You should check manually in webmaster tools or you can use open site explorer to check relevant or irrelevant backlinks.

Just FYI, there's not any one tool that can show you all of the backlinks that exist to a site, you're bound to miss some.