Great question — answering as the UphillTech team:
Unfortunately, Google is not going to help you identify bad links -- they just punish sites that have them. Neither the 404 kind or the bad neighborhood kind. It makes sense they don't help with the bad neighborhood kind as spammers could use that information ... But I don't know why they won't provide a page test for links to 404 pages. The external links are something webmasters need to keep an eye on themselves. How they do it, manually or with the help of software is of no interest to Google. But having links to irrelevant content, Malware or other unwanted content, or 404 pages is bad for your site in the eyes of visitors and Google.
Full answer by Wayne Smith: https://webmasters.stackexchange.com/a/142976 (CC BY-SA 4.0).
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