I've almost always gotten meds from my vet until my dogs have come down with old age/chronic problems. Vets are small businesses. They can't invest a lot of capital into drugs that have an expiration date. Common drugs like antibiotics, prednisone, etc. can be bought in bulk and shelved. Glaucoma medicine, probably not as much demand. It doesn't make them a bad vet because they can't warehouse rarely used drugs. The problem is not at the vet's office.
My wife’s sister’s dog got histoplasmosis and needed a frighfully expensive drug. My wife, a PA was able to get it for them for about half the price of the vet.
I don’t quite remember the details but it was all above board.