Hello Jin and thanks foryour question.
As the other Realtors have already noted, when you sell your home FSBO, the purpose is to try to avoid the sales commissions that are normally paid to both the listing and the "selling" or buyer's agent. While this often results in the seller finding an independent buyer by him/herself, there are occasions, as you have found, when you are approached by a Realtor with a client.
To answer your question, as an FSBO seller, you do not have to cooperate or pay the Realtor a commission. You did not advertise a commission, so there is no obligation whatsoever for you, as the seller, to offer or give anyone a commission. On the other hand, if you choose not to offer a commission to the Realtor, there is no obligation on the agent's part to bring a qualified buyer to you. That doesn't mean that the buyer can't find you with his/her own efforts, but it makes it less likely since once a buyer has an agent, the buyer is often more comfortable with the idea of using the agent to protect his/her position in the sale.
So what do you do? You have a couple of options:
1. Hold steadfast and not agree to cooperate. Be frank...let the agent know, as you have done here, that you don't have much money, and that you're only selling your home as an FSBO because you cannot afford to do so and pay a commission. For a few of us--I would be in that crowd--finding a suitable home for our client is worth more than the commission. If this is the perfect home, I'd be willing to step aside to allow both parties to consummate the deal without me, and this is especially true for those in the military. You may also be dealing with a similarly egalitarian Realtor, so talk with agent.
2. Negotiate a commission that you can afford. Again, be frank with the Realtor and tell him/her that you don't have much money but that you can afford "X" percentage (between 1 and 2 percent, if that's all you can muster) if the agent will agree to help both you and the buyer complete the transaction. Again, depending on how eager the agent is to find a home for the client, he or she may or may not agree to this concession. You won't know, however, until you ask.
Of course, there is the possibility that the Realtor will decide not to work with you. Since there are many "fish in the sea", I would suggest moving on. If you find that being an FSBO is not working quite as you had hoped, talk with a discount agent about sharing the job of selling your home in return for a reduced commission.
Good luck and happy house selling!!
Grace Morioka, SRES, e-Pro
Area Pro Realty
San Jose, CA