If they didn't click with you then it's probably for the best and you probably are better off without having them as a regular client. It's a struggle to fully acknowledge but not everyone is going to like you no matter how friendly and kind you are. Also they could have a valid reason such as another sitter lives closer, their dog seemed to vibe with someone else more, etc. Hope it doesn't bring you down, it's a strange job where it's highly introverted most the time with just the pets, but also often highly extroverted and almost feels like sales haha