I'm not sure you're comparing apples to apples, but I may not fully understand your transactions. If you are sending a want list, then receiving material from him for inspection, then paying, that involves higher transactional costs and more risk for him than if you select stamps on
ebay and pay the seller in advance. Your dealer has to take the time to find stock matching your list, check its condition, and wait for payment. An
ebay seller doesn't; you are doing the searching and selection, and paying in advance. So, I would say you should think about all the costs in a transaction before you decide you are overpaying.