You're absolutely right, but realistically a plummer or consultant messing around and inflating his price or screwing around will cost a few hundred or thousand

You're absolutely right, but realistically a plummer or consultant messing around and inflating his price or screwing around will cost a few hundred or thousand dollars extra. Not millions or billions except in the most ridiculous of circumstances. The main difference in this agent-principal conflict is the amount of capital one person is responsible for. It's actually very similar to the CEO agent-principal conflict.