There are many SEO agencies out there that shell out their SEO services for clients and help them gain good page ranking on the search engine results. Usually hiring a SEO director would cost more for a company as they usually 100,000 Euros per year to lend their services. On the other hand, a top-notch SEO agency will charge 100 Euros per month and they have separate teams to perform on-page optimization, technical optimization, social media campaigns and content generation for high quality link baiting.
Agencies have extensive knowledge as they work for different industries while the SEO director will have detailed knowledge in a specific domain. The agencies have many good clients who can help the website gain some quality back links.