You are free to hire an agent to represent you and help you through the process but its not likely the seller will pay them a commission unless you successfully negotiate that into your offer. It might be easier to just have your attorney prepare the docs or even a title company depending on what your state allows. @Brandon P.
You can use a realtor, but they work on commission. If the owner does not have an agreement with a broker (which he/she doesn't if he/she is doing FSBO) then you'll end up having to pay some sort of commission to the agent to compensate him/her for the time (the cost would be negotiable with whatever agent you choose, but it would be an agreement between you and the agent, the owner would not be involved in that).
Alternatively, you can just pay a lawyer to write the contract and close for you, which you would most likely have to do anyway.
I just did a deal with a for sale by owner and they did not pay the buyer's agent fee. I ended up picking up the tab. I like my relationship with my agent so I saw it fit to take up the fee if it is not covered by the seller.
A FSBO owner should sign an Authorization To Show, they do not need to sign a listing contract, but could. The listing is seller paid commissions unless specifically stated that the buyer is to pay, the ATS simply gives the agent the authorization to step foot on the property, they will represent the buyer under a Buyer's Agreement and the buyer will be paying the fees. :)