There are other ways that having the same Realtor represent both sides of the transaction can be a negative as well. Actually, the best thing for you to do when you see an advertisement in the paper is to call your own Realtor and tell them about the ad. Since addresses usually do not appear in advertisements, your Realtor will call the listing agent and find out which property is featured in the ad. It may be a great home for you, but it may also be a property the Realtor has already disregarded because it backed up to a busy noisy street and you have told your Realtor you wanted a quiet neighborhood. First you have to have a Realtor you can call.
Referrals are always a good way to go.
Perhaps a friend, co-worker, or family member recently bought a house in the same community and had a good experience. However, if they bought a house twenty miles from where you want to move, it may not be a good idea to use the same Realtor. You want one who knows the area in detail, and has already previewed many of the homes available for sale in that community. Community knowledge should be important to you because you are not just buying a house. You are buying a home.