Fame
Most people won't gain fame and fortune by becoming a pet sitter, but they might find a way to wrangle fifteen minutes of fame if they get creative. First, how many dogs can they walk at one time? Five? Ten? As many as they can string together? They might get a photo in the local newspaper, or perhaps even a brief appearance on their city's evening news as a human interest story, but only if they can manage that feat without losing any pooches (or fingers).
Pet sitters in celebrity hotspots, such as Los Angeles and New York City, often gain a reputation by walking the frou-frou dog breeds owned by publicity-hungry performers. On the down side, it's tough to get a celebrity gig if you're not hooked into the "famous person" service market. Sitters may also get hooked into the "famous dog" service market, but Lassie and Rin Tin Tin aren't in a position to be taking on clients these days.