I think majorbloodnock has things about right. The client definitely has the right to expect work of merchantable quality. They should not expect world-leading skills unless they have explicitly included this in the contract and agreed to by the supplier. A consultant should show competance in understanding the client's problem, and in researching and delivering a solution.

seagoon: "I am trying to teach you about gravity. When you jump in the air, why do you come down again instead of floating away?" eccles: "Because I live here."