This section is from the book "The Law Of Contracts", by William Herbert Page. Also available from Amazon: Commercial Contracts: A Practical Guide to Deals, Contracts, Agreements and Promises.
Unless otherwise specified, all materials shall be new and both workmanship and materials shall be of good quality. The Contractor shall, if required, furnish satisfactory evidence as to the kind and quality of materials.
The Contractor shall not employ on the work any unfit person or anyone not skilled in the work assigned to him.