I totally understand what you mean by "testing" your vet. We love our sweet babies and want them to get the best care. I actually had to change vets because I wasn't comfortable with the care my pets were getting. I had also heard from others that they had similar experiences. Sometimes it's something you observe during treatment like they're neglectful or not thorough enough. Other times it's just a feeling. The vet I go to now is twice the distance but 100% better. It is worth the trip and so reassuring to feel like my pets are being well cared for.
Word of mouth is a good way to find a qualified vet, asking around and learning about other peoples experiences. You can also check online for exotic vets and look at reviews. It's good to ask them questions, kind of like an interview. For instance....how familiar are they with gliders? How many do they care for? Are the vets and vet techs comfortable handling gliders? Do they have a hospital and are they set up for emergencies? Also, are they members of organizations like the Association of Exotic Mammal Veterinarians? In my case, since I take my parrot to the same vet, it was important to me that the vet was a member of the Association of Avian Veterinarians.
Here are some links that might help.......
www.sugargliderhelp.com/links/pages/Sugar_Glider_Vet_Database/index.html
www.vetective.com/
aemv.org/
(click on 'find an aemv vet')