Types of Listings

There are a variety of listing contracts, but very few of them are used. The most common is the "Exclusive Right to Sell," but there is also the "open listing," the "exclusive agency listing," and the "one-time show."

Open Listing

Typically, the "open listing" is used by people trying to sell their home on their own, but are also willing to work with real estate agents. The real estate agent brings potential buyers to the home, and if the customer buys it, the agent has earned a commission. 
A seller can give an open listing to every agent who comes around. 
For that reason, agents are not going to market your home or put it in the Multiple Listing Service. An agent will probably only show your home if your home fits the criteria for one of their customers. 

One-Time Show

A "one-time show" is similar to an open listing because it is most often used by real estate agents who are showing a FSBO (for sale by owner) to one of their customers. A home seller signs the agreement, which identifies a potential buyer and guarantees the agent a commission if the buyer purchases the home. This prevents the buyer and seller from negotiating afterward or trying to avoid paying the agent's commission.
Just as with an open listing, agents are not going to spend money on marketing your home, and it will not be placed in the Multiple Listing System.

Exclusive Agency Listing

An "exclusive agency" listing permits an agent to list and market your home. The agent is guaranteed a commission if the house sells through any real estate agent or company. It also permits the seller to seek out buyers on their own.
This is not a popular type of listing agreement because there is not much incentive for agents to spend money marketing your home. If you find your own buyer, they have spent money they cannot earn back through the real estate commission. Also, it is too easy for a greedy buyer to work around the agent and negotiate directly with the seller.
If you happen to come across an agent willing to accept such a listing, do not expect too much from them. More than likely, they will just place it in the Multiple Listing Service and sit around to see if something happens. A good agent would never settle for such a listing.

Exclusive Right to Sell

Permitting a real estate agent the "exclusive right to sell" your home does not mean that there will not be other agents involved. Because your agent is the listing agent, part of his or her job is to market your home to other agents who work with buyers. It will be those agents who will show your home to their customers. But no matter who sells the home, even if you sell it yourself to a friend, your listing agent will earn a commission.
An exclusive right to sell should be the only type of listing an effective real estate agent will accept. This is simply because they have a reasonable expectation of getting back the money they will spend on promoting and marketing your property. The listing contract should specify whether or not your house will be listed with the local MLS (multiple listing service). It is absolutely in your best interest to have the house listed, since your sales force is automatically multiplied by however many agents are members of the local MLS. If your house is not listed, then only one agency will be working for you instead of many.