1. The food and medicine you spend on dog will be spend more than any "human" including your wife/girl friend, and children.
2. You will spend alots of time on your dog too.
3. It is suggested to buy some professional book for particular species of the dog and read it to learn how to train them.
4. Each dog has different kind of personality, so if you breed different kind of dog compare to your friend, don't take all of their advise.
5. Spend more time on the pet, more and more. Usually the more time you spend on it, it will be more listening to your instruction.
My father got a german sepherd(spelling?). Althought supposely it "heard" to be a fierce dog, but it is some what an idiot dog while also a smart dog.
But the Chao chao that my aunt breed, it just doesn't like people to grab is from behind. Therefore, me, my sister and my mom got bite form it before and left a scare that last for one to three months
Edit: give them the food that doctor or the trainer advise, don't give them the food that human eat. Because usually most of the food we eat are too oily, too much seasoning and is bad for them, and we always don't know which kind of the food we use to eat are eatable for them.
The initial cost of your dog is going to be the biggest cash sink.
You pay for the dog, the food, the bed, the toys, the shots, they neutering/spaying, etc...
But once you have all of that done it is pretty much food. Everyone is making it seem like you have to get your dog drugged up every month, which isn't true. Sure, there will always be those "emergencies" where you are going to end up dropping a bunch of money on the dog, but more often than not the dog will be just that... A dog. If you keep it on a healthy diet, give it lots of water, keep it active, and love it, then you should be fine.
I'm gonna agree with all the people about the running thing, especially if you pick a medium/bigger sized dog. I have a german shepard and when he was 7-10 months old or so he raised hell in the house until I got him a zip line outside to run on and he goes on the line every day for 3-4 hours periodically and he is alot more calm and happy in the house.
If you have a smaller dog it will need exercise and something to do as well, but you don't need a large yard or open area as you would a large one imo. Even then I think it was an episode on just a bit ago, if the area they have is kinda small you need to walk them and keep the scenary fresh, or the dog will get bored.