Hello.
So about Lace making. Its pretty hard to call yourself a professional lace maker today. Several hundred years ago, it was probably easier.
So in this context professional just means "sells their work, full time or part time."
Fine lace (delicate, filmy) takes a while to make. It's hard to get the thin threads lacemakers used.) There were lacemaker guilds to ensure quality. (More often you had a teacher/school/vendor ensure strict quality)...