realtor's often have 3 days to 'pocket' a listing before they have to put it in the mls. these 'pocketed' listings can be privately shared and thats where realtors keep a little advantage.
its only _locked_ in if you sign a contract with a realtor (which can actually be negotiated, shop around). if you do a 'for sale by owner' you have no such obligation. even if the other party tries to use an agent. the agent will often 'ask' if you offer a 3% buyers commission, which is, totally up to you. even that is negotiable at that point. the downside is, they have less motivation for showing your house. but both times that i did, i hired a real estate lawyer to get the contracts and such, but handled the 'showing' and negotiations myself. in a hot market, a good agent can earn their % in patience and marketing.