You probably already know this, but just so we're on the same page:
From reading pharmacy discussions on VIN: it is illegal for a veterinarian to purchase a compounded drug and turn around and dispense it to a client. Period. You may write the client a prescription (or call, fax, whatever) and the compounding pharmacy may dispense the drug directly to the client. You may purchase a small amount of compounded drug for direct administration to patients in the hospital (or outpatients). You may not legally call up Big Name Compounding Pharmacy, order a metric crapload (industry term) of compounded tubes of flunixin meglumine paste, and resell them to clients as "generic Banamine". Yes, the vet who treats most of the horses at my barn (but not my friend's horses) periodically drops off (labeled) BNCP compounded flunixin paste, which comes in the same concentration and form as Banamine, and literally a case at a time of compounded phenylbutazone powder.
One issue with compounded drugs is informed consent. IME, most clients are not necessarily even told that the drug being given to their animal (or illegally dispensed) is compounded, let alone the higher risks inherent in using compounded drugs. Particularly for hobby animals and pets with a greater individual attachment, or breeding animals of some value, how many of them would ask for an alternative, approved drug/formulation if given information about the risks and benefits of compounding? This may be relevant more to horses than food animals, but I have seen compounded drugs often used for questionable justification where there IS an alternative, even if it's more expensive/not quite as convenient/etc. Sure, there are some drugs for which vets have no choice, like pergolide, which is no longer manufactured at all in the U.S. - the benefits for a Cushingoid horse clearly outweigh the risks. But what about compounded omeprazole suspensions (which are already of dubious legality since Gastrogard is a perfectly good orally dosed form, albeit expensive), which don't necessarily even work because of how finicky the molecule is (breaks down sitting on the shelf in aqueous media, has to be protected so it doesn't get degraded by stomach acid)?
Personally, when I see vets who buy compounded versions of existing drugs just because they're cheaper, and resell them to their clients for a markup, I start to wonder about their general moral character. It undermines the trust required for a healthy VCPR, since compounded drugs are NOT necessarily as safe as legally manufactured drugs. I'm not saying it makes them an axe murderer, but I wonder what other corners they might be cutting in the name of making money. It also, in my mind, calls into question the ethics of the compounding pharmacy involved. If they are willing to illegally manufacture large amounts of common drugs, what corners are THEY cutting which may jeopardize patient safety?
Just my .02 for now, I'm sure I'll think of more later.