As with any and all professions, there are good examples of the representatives of those associations and there are bad. Do your homework: study the nature of skilled tennis, (if that is what you want to become), and understand what you want to move towards. There are so many free and low cost web sites, (this one included), that you can learn a great deal about the game.
Forums like this one, (which in my opinion is one of the best in terms of quality of postings and diversity, even if there is a great deal of disagreement too!), can give you an idea of grips, strokes, and strategies that you will want to learn. At the very least, you will be able to ask the right questions, know more about what you are looking to achieve, and overall, have a better chance at getting more out of any lesson.
Of course, there are a gazzillion DVD's and books out there. Some are indeed better than others. I won't discuss any here as it would take too long. However, as a teaching pro for 35 years, I can tell you that nearly all books and DVD's offer something you can gain from.
Finally, make sure you communicate what you hope to achieve from your lessons. A good pro will ask, too. Then, be prepaired to learn some things that might come hard or are more unfamiliar. A good pro will understand this and give you drills and exercises to overcome these and master the proper patterns for progressive improvement. A bad pro will simply provide affirmation at the wrong time. For example, if my student stroked the ball with the right grip, swing pattern, footwork etc., but missed the ball completely, I would most likely complement the attempt. However, if you somehow made contact with bad form but the ball went towards the target, I would not applaud that at all. In other words, a pro looking for improvement towards a goal will not be satisfied with "instant gratification' of hitting a target if it was done with poor mechanics that won't equate into more sustained learning. (It usually was more luck than skill if this did happen!)
Hope that helps!
Dave Smith: Author, Tennis Mastery/Coaching Mastery;
Senior Editor, TennisOne; Dunlop Master Professional