"Sincere appreciation" means genuinely recognizing and valuing something or someone, expressing gratitude or admiration with honest and heartfelt sincerity. Full definition
They show sincere appreciation for hard work and extra effort. (entrepreneur.com)
Whether by phone, handwritten, or email, it is important to follow up interviews, references and other employment contacts with sincere appreciation. (livecareer.com)
They're willing to show sincere appreciation for hard work and extra effort. (inc.com)