Before signing a contract, the plumber should satisfy himself that the person with whom he is dealing is legally capable of making a contract or is duly authorized. If the person is not of age, is mentally unbalanced, is a banknipt, and in some states is a married woman, the contract is void or voidable. Time, worry and money will be saved in such cases by taking up the matter with the natural or appointed guardian and have him sign the contract.

In the case of municipal, state and national governments, likewise in the case of corporations, some one officer is authorized to sign contracts similar to those for plumbing work, and before entering upon the performance of the contract, the plumber should satisfy himself that the right person had authorized him to proceed. Sometimes the plumber has to deal with the agent of an owner, in which case he must make certain that the agent is duly authorized in writing. Indeed, it is questionable if the authority of an agent to sign contracts for work affecting real estate would not have to be not only in writing, but sealed and acknowledged.

The architect is usually an agent of the owner, authorized to order new work and obligate the owner to pay the cost. Sometimes he is authorized to sign contracts, but that must be a specific authorization, not an implied one, in order to bind the owner. In public work, on the other hand, the architect has no authority to order changes or extras. If he does so, there is nothing to prevent those in authority from ratifying his act, but usually it is best to secure a written order for all extra work from the commissioners in charge of the building operation.