There is not certification, and I hear this all the time.
The key is the training that will attest to the dogs ability to perform whatever is needed per the ADA law. Letter from the trainer and a doctor are always helpful.
The airlines, who are becoming very $$$$ interested has asked more all the time - the last 3 times I have flown than ever before. I now carry papers with not just my doctors letter but also copies of the testing that has been done.
The issue is that there are folks with pets who are passing them off as service dogs. Businesses and airlines and such are starting to challenge that. The ADA is aware of this issue, as well.
No one may ask what your specific disability is but they may ask what tasks the service animal performs for you. The last time we traveled by air and I was challenged I finally asked the airline clerk who was questioning me to please throw the clipboard she had on the floor - she did and Cali did her thing - no further questions asked!
Then I told her the story of the time Cali alerted me to the massive amounts of water that was flooding the bathroom of the plane. We gotta free ticket for that because, as the captain of the plane told me, by the time they had found the leak it would have been so bad they would have had to divert the flight. Those little Yorkie ears listen for everything - just as she has been taught.
I also carry a card with the ADA laws printed on it for education purposes.
Hang in! Again the training is the key - the place that trained Cali has gone to bat for us sucessfully so many times.
I always show up early so I have time to deal with this. I do not have a disability that you can see when I walk in the door and people do not see 4 lb Yorkies as service dogs!
Just last month she smelled smoke and heard a fire crackling that no one else had heard and we had the floor of the assisted living facility evacuated before the fire people were there
Sorry, just can't help from telling the great stories about her