DON'T BUY A DOG IF YOU 
DISLIKE DAILY EXERCISE.

Dogs need exercise to maintain the health of heart and lungs, and to maintain muscle tone. Don't choose a breed famous for a mellow, laid-back disposition, thinking you can avoid exercising your dog.  All dogs need daily exercise of greater or lesser length and vigor. If providing this exercise is beyond you, physically or temperamentally, then choose one of the many small and energetic breeds that can exercise itself within your home, apartment or fenced yard. Most of the Toys and Terriers fit this description, but don't be surprised if a Terrier is inclined to dig in the earth since digging out critters is the job that they were bred to do. Cats can be exercised indoors with mouse-on- a-string toys. Hamsters will exercise themselves on a wire wheel. House plants and fish don't need exercise.

DON'T BUY A DOG IF YOU BELIEVE THAT DOGS SHOULD RUN "FREE."

Whether you live in town or country, no dog can safely be left to run "free" outside your fenced property and without your direct supervision and control. The price of such "freedom" is inevitably injury or death: 

• from dogfights

• from wild animals

• from automobiles

• from the local Humane Society or Animal Control 

• or from justifiably irate neighbors.  

A dog allowed to run loose is destined for disaster. A thoroughly obedience-trained dog can enjoy the limited and supervised freedom of off-leash walks with you in appropriately chosen environments. 

If you don't want the responsibility of confining and supervising your pet, then no breed of dog is suitable for you. A neutered cat will survive such irresponsibly given "freedom" somewhat longer than a dog, but will eventually come to a grisly end as well.

A better answer for those who crave a "free" pet is to set out feeding stations for some of the indigenous wildlife, such as raccoons, which will visit for handouts and which may eventually tolerate your close observation.

DON'T BUY A DOG IF YOU CAN'T AFFORD TO BUY, FEED, AND PROVIDE HEALTHCARE FOR ONE.

Few breeds are a cheap to purchase, as running a careful breeding program with due regard for temperament, trainability, and physical soundness (hips especially) cannot be done cheaply. 

The time the breeder should put into each puppy's "pre-school" and socialization is also costly. The "bargain" puppy from a "back-yard breeder" who unselectively mates any two dogs who happen to be of opposite sex yet same breed may well prove to be extremely costly in terms of bad temperament, bad health, and lack of essential socialization. 

In contrast, consider the occasional adult or older pup available at modest price from a disenchanted owner or from a breeder, shelter, or rescuer to whom the dog was abandoned; most of these "used" dogs are capable of becoming a marvelous dog for you if you can provide training, leadership, and understanding. 

Whatever the initial cost of your dog, the upkeep will not be cheap.  Dogs are living animals who require quality food and abundant water.  (Need I add that what goes in one end must eventually come out the other?)

Large dog breeds tend to have larger veterinary bills, as the amount of anesthesia and of most medications is proportional to body weight. Spaying or neutering, which costs more for larger dogs, is an essential expense for virtually all pet dogs despite their "pedigree", as it "takes the worry out of being close," prevents serious health problems in later life, and makes the dog a more pleasant companion. 

Most breeds are afflicted to some extent with health conditions which can be costly to treat. Your best insurance against genetic disease is to buy only from a litter bred from a responsible breeder.  

Professional grooming, if you use it, is expensive too. An adequate set of grooming tools for use at home adds up to a tidy sum, but once purchased will last many dog-lifetimes. 

Finally, the modest fee for participation in a series of basic obedience training classes is an essential investment in harmonious living with your dog; such fees are the same for all breeds. The modest annual outlays for immunizations and for local licensing are generally the same for all breeds, though some counties have a lower licensing fee for spayed/neutered dogs.

All dogs, of whatever breed and however cheaply acquired, require significant upkeep costs, and all are subject to highly expensive veterinary emergencies. Likewise all cats.  

Hamsters usually don't warrant such trips to the vet, and sick fish are usually doctored either at home via advice from the teenager at the local pet store.  Some fish are even "treated" by a trip to the local sewage treatment center via the commode.