Darrin Black has parlayed his one-man shop into a company with eight locations in West Texas on the strength of one basic operating philosophy: Invest in as many different kinds of equipment as possible.The way the 51-year-old master plumber sees it, the more kinds of equipment his company owns, the more services he can offer. And the more services he can offer, the more likely it is that he can get a foot in the door with customers. And if he provides great service along the way, those customers will call again when they need something else.Black had no grandiose
