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Make sure you know where the food is kept and how much the dog is typically fed per day. Ask about their favorite treats and how often they're given treats. You should also ask about food allergies and any digestive problems the dog may be prone to. Some dogs require dietary supplements or medications so be sure to ask about that as well. Never feed a dog chocolate, grapes, milk, cheese, onions, nuts, garlic, yeasted bread, avocados, or anything with caffeine. If you feed it an apple, make sure you remove the pit as it is poisonous for canines. All dogs need to be walked daily but some need more exercise than others. Ask the owner about the dog's exercise routine and how often there are walked. Some dogs like the familiarity of their walking route so ask where they are taken as well.  In addition to exercise, you may want to take them to a dog park where it can run around freely and socialize with other dogs. You should also consider researching exercise needs for specific breeds. Dogs often have unforeseen medical crises so you'll want to be prepared. Make sure you ask about past health problems and research health problems associated with the dog's breed and how you should handle them. You may vet records in case you need to take the dog to a pet hospital during an emergency. If you have to give the dog medication, ask how it's typically delivered. If you have to give them pills, it may help to crush them or hide them in food. Proper dog training requires consistency and you can mess up the dog's behavioral expectations by giving them treats too often or giving improper commands. Ask about how the dog has been trained and how you should react to good and bad behaviors.  You can also reinforce their training by giving them commands they've already learned and rewarding them appropriately. Make sure to ask if the dog is good with children and strangers if you foresee it interacting with them.
Determine their dietary habits. Determine their exercise needs. Ask about the dog's medical history. Determine their level of training.