The situation you are asking is regarding dual agency or buyer representation. It is not necessarily cheaper. If you use the Seller’s agent to represent you as a buyer, you have a dual agency agreement. Some states do not allow this.
In essence, one agent has agreed to represent the best interests of BOTH parties in the purchase. Cheaper, nope. The agent receives commission for the selling and buying side. In most states, or how the agency agreement is written, the seller pays the commission for the Buyer’s agent as well as the Seller’s agent. If you feel as though you want to make sure that an agent is soley concentrating on your best interest, my suggestion would be to have a separate buyer’s agent.