Generally, it is always proper to use a person's profession as a title/form of address. If one is uncertain, "good man/woman" is a safe alternative, unless the person feels snubbed at your failure to perceive his or her proper status.
The titles "Lord" and "Lady" are used solely for nobility
(status 3-6) and their children (status 3-5).
The titles "Sir" ("Sieur") and "Dame" are used for gentry (Status 2-3) and their children (Status 1-2).
"Master" and "Mistress" are similarily reserved for craftmasters and other people who command a number of subordinates (status 1). Master is also the proper term for a gentleman without noble blood.
"Freeman" ("kar") is proper for any free commoner (Status 0 or -1).
People of the lower classes (Status -2 or less) are fortunate if they are addressed by name, much less title. "You" or "servant" are the best they can hope for.
Many people of status refer to any male commoner whose name they do not know as "Jack".
Calling a man a "knave" indicates that one considers him dishonest, rogue is a stronger word.