Many property flippers buy directly from the owners. They find properties in many ways, bird doggers, direct marketing, bandit signs, etc.
If you are buying your parents home with a mortgage, DO NOT use a realtor. Someone will make 6%+, and it will not be you or your parents. Just put together a sale agreement, and go to a title company. The mortgage company will need an appraisal, and go with that price. They need to sell at Market. If you went with a realtor, it would not change the appraisal.
If you are paying cash, make the transaction for 6% less. No realtor means your parents will have the same take-home as a sale with a realtor.