Hardy boys The Vanishing Thieves by Franklin K. Dixon

Frank and Joe regarded the raised wretch warily. "I said what are you doing here?" the workman repeated. We, eh, we're looking for jobs," Joe replied, hoping he could talk his way out of the situation "The front door was locked and nobody answered, so we came in the back way. We thought this was the hiring office, but i guess it isn't." The workman looked them over suspiciously. " what made you think we needed help?