Builder's sales reps are not REALTORS, nor even licensed real estate agents. They owe zero fiduciary duty to you, the buyer. They work for the seller (builder). Here in Erie there are sales reps blatantly LYING to buyers about oil and gas fracking operations going on.
By all means, DO have a REALTOR working for you. It doesn't cost you anything. Their commission is already built into the builder's marketing budget. You won't get any sort of discount on the home by not using an agent.
Metro Brokers | Grenier Real Estate