Always buy "certified seed". This is identified by a blue tag saying certified. By spending a few extra cents up front, you will save many hundreds of dollars along with the added aggravation of controlling unwanted weeds later. Choose the right grass seed, sod or sprigs for your situation.
Start by asking family and friends if they can recommend an agent. Compile a list of several agents and talk to each before choosing one. Look for an agent who listens well and understands your needs, and whose judgment you trust. The ideal agent knows the local area well and has resources and contacts to help you in your search. Overall, you want to choose an agent that makes you feel comfortable and can provide all the knowledge and services you need.