I recently talked to a lady who had adopted a six month old Springer Spaniel puppy. Its previous owners had installed a new lawn, and when the dog started digging in the lawn, the father insisted the dog had to go. Don't ask me why that family got the dog in the first place, but the dog is now much happier with its new doting owner. When you adopt a dog either directly from an Animal Shelter, or through a rescue organization, you will normally be expected to pay a small fee to cover the cost of the dog's vaccinations and any expenses incurrred during the rescue process. You will almost always be obliged to get your new pet neutered if it is not already.
Many vets offer free initial medical inspections for adopted animals.
These groups actively seek out unwanted, abused, or neglected pure bred dogs and try to find new homes for them. There are also many rescue groups who help find new homes for cross bred dogs. This approach takes some of the trauma out of adopting a dog. You don't have to go directly to the animal shelter, which can be a painful experience. You usually get to meet the dog after it has been cleaned up.