Spam blogs have been increasing in number and frequency since marketers discovered the importance of SEO. Google still puts a very high value on these all important backlinks. "A backlink is a link one website gets from another website. Backlinks make a huge impact on a website's prominence in search engine results. This is why they are considered very useful for improving a website's SEO ranking. Search engines calculate rankings using multiple factors to display search results." Having content
produced for you and linking back to you is a good thing! You just have to make sure that the posts are genuine or informative blog posts rather than spammy. Depending on how often your site is being linked to and how much guest content is being produced this can be overwhelming. Some sites have thousands and thousands a day. Its an awesome feeling when you get a few genuine guest blogs and it helps your SEO skyrocket. So the here's the catch. If you don't stay on top of guest blog monitoring and let spam build up, google drops the hammer. Sites that accept guest blog posts put themselves at risk of being penalized/filtered by Google; as Google has said over the last couple of years that they are cracking down on spam and will continue to crack down. Guest blogs spamming you can be devastating. I have seen Google put several businesses devoted entirely to guest blogging out of business. Spamming is used by sites with crappy content and poor SEO in an attempt to get links.
If you want to get links to your site that are actually worth having, write GREAT content, build GREAT tools, or create some kind of GREAT resource that can't be found on thousands of sites that other webmasters want to link to, rather than looking for ways to "plant" links on other sites pointing back to yours. This is the ONLY long-term strategy that will not eventually result in penalty/filtering by Google. Developing great B2B marketing is based around content because of the long term turn around. Its critical to be sure that all the hard work put into creating content isn't ruined by a few lazy seo attempts from others. This spam is essentially trying to hijack your domains hard earned authority.
Moral of the story:
Guest blogging can benefit both parties - The host gets an article and the blogger a link/reference. However, if the owner of the site doesn't have the resources/time/manpower to check the blogger credentials, it's safer to stop accepting guest blogs altogether. If you can stay on top of guest blogs spamming you, continue to accept guests articles to dramatically increase your website authority.