If you look at your top competitors, you may notice the same person or company is running multiple websites, making it difficult for you to compete. They're there on page one and two of the SERPs because the person operating the sites created an effective link circle.
A link circle isn't the same as a private blog network with all the sites linking to the money site. Google frowns on PBNs since the sites are build solely for the purpose of linking to another site.
Building Your Link Circle
Building a link circle isn't easy. You have to build multiple websites in the same niche with each one focusing on a specific part of the niche. If you choose gardening as your niche, creates websites about flower gardening, growing vegetables and so on. This tactic is super effective for dominating the search results. If you want to link each sit to all of your other websites, do it the right way. The key is transparency; let visitors know the links send them to your other websites.
Each site in your link circle has to have high-quality content. If you have thin content, Google may penalize you for creating sites solely for link building and without value. Accept high-quality guest posts to add value to your site with additional content which your visitors would enjoy.
Establish Your Authority
Establish your credentials to operate the sites; Google will see the site as authoritative and the links will have more link juice. Establishing your authority can be as simple as gardening all your life and being part of a gardening club or volunteering at your community garden. If you accept guest posts, list the authors credentials.
If your competitors are using a link circle to dominate the search results, get to work building your own niche websites. For more information click here https://www.reddit.com/r/SEO/comments/c8cdru/competitorsused6differentdomainsandeach/.