As those that answered prior have mentioned, most FSBO homes are not priced in accordance with the market. They (generally) price on a "need" basis versus a "market" basis and after trying to go on their own, eventually turn to a professional to list their home. Bear with me here as I go over some basics...there's a method to the madness!
The listing agent, after a listing agreement is signed, then has the responsibility to market the property everywhere they can and to make sure that every avenue is taken, represent the seller and have a fiduciary responsibility to the seller. Internet, Open Houses, mailings, Brokers Open Houses, phone calls and to make sure that every possible agency relationship that exists (buyers agents, sub-agents and transaction brokers) get compensated for bring the buyer. The listing agent should not care where the qualified buyer comes from and should compensate any agent for the qualified buyer.
I'm sure you know of the sellers agent agreement that is also called the listing agreement.
There is a similar agreement for Buyers Agents. As a contracted Buyers Agent, the responsibility of that agent is to look everywhere for the home that meets your wants and needs. EVERYWHERE! FSBO's, expired listings, mailings, door knocking, phone calls in accordnce with the Do Not Call Registry. So a buyers agent agreeement is like a sellers agreement which specifies a fee to be paid at closing regardless of the homes listing status and to have that same fiduciary responsibility to the buyer. They will work on YOUR behalf and find the right property for you. According to National Association of Realtors, a FSBO is (on average) priced about 15% above market, and if you as an unrepresented buyer are not armed with the market data, knowledge and negotiation expertise represented by an agent you could actually be overpaying. Most FSBO sellers will pay a realtor fee but these need to be found by your Buyers Agent. But what if your perfect home seller won't pay the fee. Well, if your buyers agent beats the bushes, finds the perfect home and property (even if was not listed or even if the sellers had not thought of selling), negotiates to a MARKET price and terms you agree to, coordinates and guides you through the maze of getting to the closing table, they have fulfilled the Exclusive Buyer Agency Agreement that you enter into and have earned their pay.
Summary: If you have full faith and trust in the agent you are working with, allow them to work outside of the constraints of MLS or only those FSBO's that will pay the fee. After all...your perfect home at the best possible price and terms is your goal and now it is your agents goal regardless of the sttus of that home..knowing he/she will be compensated for their work. Unlike most every other profession, a Real Estate Agent ONLY gets paid upon the succesful completion of the task (closing). Your dentist, CPA, doctor, lawyer, contractor, will be compensated based upon the percentage of work completed. Heck, your heirs will get a bill from the anesthiologist even if you don't make it through the operation. Your agent only gets paid by their Broker if everything is a success.