Which of the following is NOT a way to build backlinks?

Buying backlinks is explicitly against Google's Webmaster Guidelines and can lead to penalties, making it an unethical and risky practice for building backlinks. While it might seem like a quick solution, the long-term consequences outweigh any short-term gains. Creating linkable assets (valuable content that naturally attracts links), reaching out to unlinked brand mentions (asking sites that mention your brand without linking to add a link), and guest blogging (writing content for other websites that includes a link back to your site) are all legitimate and ethical strategies for acquiring backlinks. These methods focus on earning links through value and relationships, which aligns with search engine best practices.