Determining whether you are being underpaid requires considering various factors such as your location, industry standards, job responsibilities, and years of experience. While I cannot provide specific references or examples, I can offer some general insights.

1. Industry and Location: Salaries can vary significantly depending on the industry and location. For instance, the average salary for an SEO Manager can differ between different sectors or cities. Research industry-specific salary surveys or consult salary comparison websites to get a better understanding of the average pay for your role in your specific location.

2. Years of Experience: Your 4.5 years of experience should be taken into account when evaluating your salary. Generally, as you gain more experience, you become more valuable to employers, and your salary expectations tend to increase. Compare your current salary with the average salary range for SEO Managers with a similar level of experience.

3. Job Responsibilities: Managing over 30 clients directly, handling web development tasks, PPC, and having two direct reports are significant responsibilities. If your role encompasses a wide range of tasks and requires a high level of expertise, it may warrant a higher salary. Compare your responsibilities with similar job descriptions in the industry to assess if your compensation aligns with the market.

4. Company Size and Resources: The size and resources of your company can impact your salary. Larger companies often have more budgetary flexibility and can offer higher salaries. Compare your salary with what other companies of similar size and resources are offering for similar roles.

5. Performance and Achievements: Consider your performance and achievements within the company. If you consistently exceed expectations, deliver exceptional results, or have received recognition for your work, it may be an indication that you deserve a higher salary.

Ultimately, to determine if you are being underpaid, you should conduct thorough research on industry standards, consult salary surveys, and compare your compensation package with similar roles in your location. Additionally, consider discussing your concerns with your supervisor or HR department to gain further insights and potentially negotiate a higher salary if appropriate.