There was a time, back in Tango's Golden Age, when there were no professional Tango teachers. You learned Tango from your father, your uncle, your brother, from watching your parents and their friends dance.
With the renaissance of Tango in the late '80s and early 90's, there also grew a class of professional Tango teachers. Some were stage tango dancers who supplemented their income by teaching Tango. Some were traditional dancers who found they could make money teaching people (mostly tourists) to dance Tango. Some had a strong background teaching other forms of dance; some had never taught anything in their lives.
The difference between professional and amateur Tango teachers is quite simple: Professional teachers get paid.
Getting paid does not automatically make you a good teacher. I have known a number of amateur Tango teachers who are better teachers than some of the paid professionals.
But generally, when we talk about amateurs teaching any skill, there is an implication that amateurs are less knowledgeable and less capable than people who teach for a living. And certainly there is some truth to this. If you charge for teaching a skill or an art, you had better be good enough to give value for the money. If you cannot give value, very soon you will find you do not have students.
So what about amateur Tango teachers? Should they be discouraged?
What, even if they are not good dancers or teachers?
The most important thing a teacher can convey to a new Tango dancer is an appreciation of the dance, a love of the music,and a desire to know more. This can be shared by the newest beginner as well as by the most experienced teacher.
So what, then, is the problem with amateur teachers? The main problem is that they have a tendency to confuse or overwhelm the new dancer - especially new leaders. This is the number one cause of new Tango dancers giving up too soon. Experienced teachers know how to avoid this problem by properly pacing classes or lessons.
Amateur teachers can also misconvey information that they have misunderstood from classes or videos, leading to the sharing of bad habits. I remember many times when a new dancer showed up at a milonga, saying "I have been learning Tango with so-and-so amateur teacher" and a part of me shudders. But the larger part of me recognizes that the amateur teacher taught his student enough that he felt comfortable enough to show up at the milonga and dance.
Bad habits can be fixed. And an enthusiastic Tango dancer is usually happy to extend his or her knowledge.
I think on balance, the enthusiasm advantage outweighs the disadvantages.
Ideally, someone who wants to learn Tango should find an experienced teacher, whether professional or amateur; someone who is good at conveying the necessary knowledge, and whose students are a pleasure to dance with. But one can also learn from every partner, and at a practica one can learn from other dancers.
So, professionals, do not discourage or denigrate your amateur teachers. They are a powerful force for growing a community.