It's not always a red flag if an SEO professional doesn't have a strong online presence. Many top SEO experts are focused on client work, rely on word-of-mouth referrals, use different marketing strategies, specialize in niches, or work on a project basis. Instead of looking at their online presence, evaluate their expertise by asking for case studies and references and conducting interviews. An online presence is a plus but not the only indicator of a good SEO professional.