It is common for an agent from one company to list a home for sale and an agent from another company brings in the buyer. It is called broker reciprocity. When your home is on the market and listed with a REALTOR thousands of local agents are competing with each other to find a buyer.
Broker reciprocity works because of the promise to pay the buyers agent. The agent who represents the seller charges a commission and shares it with the buyer’s agent who may end up getting paid more than the seller’s agent.
As far as I know, this type of arrangement is unique to real estate sales.
Often the agent who actually “sells” the house isn’t the agent who listed it and put the sign in front. The listing agent gets his or her name on the sign but the buyer’s agent does not.
People who are buying or selling a home are not required to use a real estate agent.
If you search for homes for sale on the internet usually the fine print on the bottom of the page will say that the listing is provided courtesy of XYZ company.
The days when only a real estate agent knew about homes for sale are long gone, yet we still add value to the process because an experienced agent has worked through many home sales. Finding a house that is for sale is one small part of the home buying process.
The home buying process should be more transparent than it is. If you are buying real estate and working with a buyers agent ask questions. Most people do not buy houses all that often.
Also, see Agency in real estate