For my eBay hobbies I use the local post office for despatching items. The staff up there deals with customers, easy and awkward all day. Even though I know how they feel since I too work with customers. I gave them a present and a card to say thank you for your help. They loved it, were very grateful and appreciate it. When you see someone regularly behind the counter serving customers day in and day out, say thank you or hand them a small present. It will go a long way even though it’s a small thing.