Why should I buy flea/tick/heartworm preventives from a veterinary hospital when there are other, cheaper places to get it?

If you purchase preventives from sources other than a veterinary hospital or a website affiliated with a veterinary hospital, you don’t have any guarantee that the product is authentic or that it has been stored and shipped properly.  Also the pharmaceutical companies will not back their product unless purchased through a licensed veterinarian.  Also when you order from your veterinarian, you’ll have the added benefit of being able to rely on his or her expertise and knowledge of your pet’s medical history.