I can relate. My vet has only given me one piece of bad advice and it was that chins may eat a small amount of leafy greens. I told him I was not going to do that and he said that was fine, that it wasn't necessary to give them veggies just that they can have a small amount of them. I didn't get into an argument with him about it, since I only owned my chin for less than two weeks but knew that fruits and veggies were not safe and it was my first visit. Otherwise I really like him, but that will always stick with me. I had actually forgot he said that to me for a couple months because he is an otherwise seemingly knowledgeable vet.
I guess they can't be perfect. Vets can't know everything and some are very willing to collaborate with their clients and learn from them. I just try to look at how knowledgeable they are in areas I am not, like surgery or meds. After researching and corroborating their advice, I can slowly build trust in them but I've never taken a vet at their word. Or anyone for that matter. I see them more as consultants and occasionally surgeons when I need them to be. A lot of these vets probably don't own chins, and it's not easy to go to a farm and observe and study them, so they would only know the technical aspects of these animals, not exactly everything to apply in their everyday husbandry.
I agree that to advise something that is wholly detrimental to your animal reflects very poorly on their grasp of the species. I would suggest finding vets that have successfully neutered chins before and are familiar with it. Other than that you can do your whole finding the right vet process after if he needs to get neutered soon. At least you won't have that to worry about and you can put more effort into looking and asking around for a regular vet.
