Choosing a realtor should be a lifetime choice, just like choosing your dentist or accountant. Realtors are on double duty as once you have bought or sold with one, and had a good experience, plan on using that realtor in the future and recommending that realtor to others. Once the loyalty is established you'll be amazed at how good your relationship with your realtor can be.
Lastly, and most importantly, you are entrusting your Realtor with your biggest asset. Your Realtor needs to be upfront and transparent in all that they do and should conduct their business in a sincere and trustworthy manner at all times, no matter what the consequences.