a good professional ballroom dance instuctor is certified first in a bronze leval then its up to them to get certified in silver and gold. organizations like the NDCA have information for them to get certified to teach. Then you have instuctors that have been tought in studios, they also are qualified but then it depends if they are active in competitions and or doing shows.....etc...you can really tell right off the bat.. who is a trained dance professional...just look how they teach and or dance. remember this...you have teachers and then you have prof. dancers that compete and have no time to teach much. who do you think can teach? answer your own question
keep dancing....by a prof.