This is a really interesting thread.
Service animals is a really hot topic with most of the trainers I know. I have been asked many times to train a service dog, but I always decline those clients. First of all most people dont' have the money to pay for 2 years of constant training it would take to have the dog trained privately. I added up my costs for that once, and I only charge $35-45/hr for a lesson (so I am very inexpensive compared to other trainers in my are who charge $85-150/hr). For two years of training it would cost about $60,000!!! And could be a whole lot more depending on what the client wanted.
I think there should be a universal "test" for service animals no matter what the animal is there for. All service dogs should be stable with no social temperament problems. Be trained to a specific level of obedience, and have training for these things regularly. I have issues with some people claiming their dog is there for emotional needs when the dog is obviously not trained, not socialized and not really a "safe" dog for large public venues such as eating establishments, grocery stores, ect.
Several months ago I was in Lowes, there was a blind woman there with her dog. This was a great sight to be seen, the dog was doing its job very well, calm, collected, on alert for obsticles. Obviously this dog was doing his job -- BUT-- then another customer came in with is small mixed breed dog. I watched intently as this small breed dog began posturing to this Service lab. As they approached eachother the owner of the mixed breed didn't do anything about it though he tightened his leash in a "oh boy not again" kind of way. The handler of the service dog was apparnetly used to her dog reacting too because she heard the mixed breed dog bark, then she tensed up too. This Seeing Eye dog lunged for this small dog, barking, scrambling his feet on the floor and in general acting rediculous.
To me, no matter how well the dog did without another dog around, this dog was pretty much useless. I don't know if this service dog was a victim of poor handling and training, or had a bad temperament. But either way this was something that had been going on for a long time.