I make recommendations to clients with every visit. It may be about vaccines, the kind of heartworm prevention they should use, which foods to feed, and so on. My opinions are based on four years of medical school, 18 years of practice, over 300 hours of continuing education over the years, and countless journal articles. I'm not perfect and I don't know everything, but I'd like to think that my knowledge base is pretty comprehensive. This is why it still surprises me when someone believes a breeder or pet store clerk over their veterinarian.
I've run into many situations where a breeder tells a client "whatever you do, don't let your vet do XYZ!" Some of these breeders are quite vehement about their opinion, frightening the client into compliance. "Your vet will tell you to do this, but don't do it! I've been breeding for 30 years and I know dogs! This is very harmful and your vet is just trying to make money and doesn't care about the risks!" Yes, I've heard these very words, and even seen similar ones written on papers given to a client when they purchase a puppy. I have to sigh and shake my head, wondering at the influence that the breeder really has. And they do have considerable influence, because I've had clients disregard my words and recommendations based on what the breeder told them.
Similar things happen with pet store clerks. I'll talk about food choices, and make some strong recommendations based on what nutritional specialists have said to me. The client then goes to the pet store and pick something else because the clerk said that what I suggested was bad.
Let me be clear. Not every vet is right, and not every breeder or clerk is wrong. But stop and think about this situation for a minute. On one hand we have someone with a medical degree and years of experience, plus mandated continuing education every year and with subscriptions to multiple scientific journals. On the other hand we have a breeder who "knows dogs" and visits internet forums. Or we have a clerk that's worked in the pet store for a few years but hasn't had any formal training in the subject. Who does it make sense to believe? The person who studies immunology at a cellular level, or the person who reads a lot from like-minded people online? The person who has learned the microscopic structure of the intestinal lining and how nutrient absorption works, or the person who has attended an at-work seminar?
If you're doubting your vet because a non-vet told you something, stop and ask yourself why. What training or experience does the non-vet have that trumps the training and experience of vet? I can bet that most vets can run rings around the non-vet with actual data and studies, rather than just relying on "years" of breeding/working/experience. Feel free to question your vet (in fact, I encourage it), but in the end stop and realize who really has the best background to make recommendations for your pet.