Every master daily handles bunch of messages, orders, requests, etc. Some of instructions rather simple, but some require careful attention and master often in doubt whether his decision to obey is a correct one.
Per Hewson J in The Makedonia  2 Lloyd’s Rep 316 at p.337:
The certificate of competency is taken by all who have given evidence on this point before me as being proof of technical ability, but all these experts laid stress in varying degrees upon the desirability of a proper interview, an interview in which to assess the applicant himself. Naturally, the length of the interview depends to a large extent upon both the interviewer and the interviewed and no hard and fast rule can be laid down. Written references are not so important as a report from previous employers. If there are no written references then reports from previous employers become very important. There are many matters to be taken into account, such as evidence that the man served for a considerable time in one ship or served the same owners in different ships for a considerable time
In my view, the least that should be done is to ensure a careful inspection of the seaman’s book, to study the history of the applicant and to question him about it and the reasons why he left his former ships; if, for example, he appears to have sailed one voyage, one owner. The certificate ought to be sighted-the certificate might have been suspended. Inquiry should be made of previous owners and, if the report says "nothing against him", to press for fuller information. I cannot imagine anything more damning than a report from a previous owner that he had "nothing against him." If nothing confidential is forthcoming the man should be interviewed until the interviewer is reasonably satisfied about him and, if he is not satisfied, he should reject him. Such important appointments to such responsible positions call for a proper interviewing and a proper inquiry.
In Robin Hood Flour Mills Ltd v N M Paterson & Sons Ltd (The Farrandoc)  2 Lloyd’s Rep 276 at p.282:
Even after making such inquiries he would inquire how far the man’s experience fitted him for service in the particular ship and take steps to see that the man was adequately instructed with respect to any features of the particular ship with which it was necessary for him to be familiar to properly discharge the duties of his position and to avoid damage to the ship and her cargo.