What you're describing is less a statement on moats and more a statement on markets. Plumbers in one location share the market (the potential clients in that area), and as the parent comment states, there is no moat in that given market. A moat is a barrier to compete within a given market. So if something made it really difficult for a new plumber to serve an already-served clientele, that would be a moat. But individuals on the other side of the planet are by physical encumbrance not actually clientele... they're not even in the market.