The current trend is to “adopt” a dog from a shelter or a rescue.  Is it possible to find a good candidate for a service dog at a shelter or rescue?  Perhaps.  However, there are a lot of negatives you need to be aware of.   

First and foremost, temperament!   I can’t stress this enough.  People will go to the shelter, see a dog that they like the size, color, type, etc and take him home and he turns into either Cujo or hides under the bed and is terrified.  Needless to say, neither of these would work as service dogs.   Unfortunately a lot of dogs are turned in for temperament problems…from bites to problems with other dogs.  

FYI, remember this….3 days, 3 weeks and 3 months for shelter dogs.   In 3 days the dog will start to adjust.  Shelters are a horrific place for dogs and they need an adjustment time.  In 3 weeks you can see their personality and start to see how much work you may have to do to have a happy, well adjusted pet.   3 months will tell you what you have.  If there are bad habits like dog aggression and you’ve made very little progress, even with a Professional Trainer, you’re probably in for the long haul.  Management in this case is your best option. 

 I will add to this discussion soon.