First, we NEVER link to a direct competitor in the same market as you and we only link to other cleaning service websites.  Each link is to content that is relevant to the content of your article.  For instance, if you have an article about how to deep clean a bathroom the link will be to another article with bathroom cleaning tips.  Relevance is key and if the link is relevant it actually boost the authority of your article in terms of how search engines will see it.