Regardless, you should have your own representation. If the firm is reputable, and you don't have your own agent, ask the listing agent to recommend someone in his/her company to represent you. Better yet, ask around and get some referrals from family/friends/co-workers who have had positive experiences with their realtors.
Keep in mind that the seller's agent is looking out for the best interest of the seller....not you. You have the right to be looked out for exclusively, and it shouldn't cost you anything extra to have your own representation!