I'm reminded of an incident... someone came in and asked the senior Sifu what his qualifications were to teach. He answered "what are your qualifications to ask?"
Seriously?! He totally said that to a prospective student?
I'm realizing I'm really blessed to find this new teacher. He had no problem full on telling me his entire lineage, qualifications, his teacher's name and time in art and teaching.
And no problem talking my head right off with in depth, educated and thorough answers to even the simplist of my WC questions about his style, lineage or his perspective on teaching.
Ask your teacher current or prospective lots of questions. Every question you can think of. They should be happy to answer and take the time to fully explain and share their wing chun knowledge.