Personally, I don't think vets are in it for the money, that's a lot of schooling, and they see so much heartbreak, I think vets are one of our unsung heroes.  There are exceptions to every rule, but I think this is very rare indeed.  Regarding treatment for Giardia, this site explains that while Flagyl takes ten days of treatment, however a newer drug, Panacur, takes only two to three days.  Flagyl has much more serious side effects, while Panacur is safe even on puppies as young as 6 weeks, and will also treat roundworm, hookworm and whipworm.  So if this is what you vet has given your dog, I would feel very confident.  Also, remember that part of his choice was made because your dog is symptom free.
   Quote:
   | There are several options of treatment, some with two- or three-day protocols and others needing seven-to-10 days to complete the job. Flagyl (Metronidazole) is an old stand-by treatment for bacterial infestations that cause diarrhea and is about 60-70 percent effective in curing giardiasis. However, Flagyl has potentially serious side-effects in some animals, including vomiting, anorexia, liver toxicity, and some neurological signs, and it cannot be used in pregnant dogs. In a recent study, Panacur (Fenbendazole), which is approved for use in treating dogs with roundworm, hookworm, and whipworm, has been shown to be effective in treating canine giardiasis. Panacur is safe to use in puppies at least six weeks of age.  Dog Owner's Guide: Giardia |