We sold our own farm, I had it listed with an agent for 6 months with them showing to the wrong type of people ( we dont really want a 2 story house-it was 2 story before they came to look & will be after they buy etc...) anyhow, I put together a website showing the farm, advertised the crap out of it & sold it to some nice folks. I figured what we wanted to sell the farm for before the agent listed it & they agreed to the price & I actually got full asking price for it. I did research through local real estate magazines, papers & on the internet to what a farm like ours would be valued at. I added & subtracted based on what other places similar had or didnt compared to ours. That is how real estate agents come up with suggested selling prices, by comparing other farms in your area that are selling, or have sold in the past 6 months. That is what you need to do. But if you are not going to use an agent, you need to find out what you have to do to sell your property, there are land plats you need to provide showing easements & restrictions, find out if your septic is up to selling standards, as is your water ( if on well) & then make sure that your property looks its best & all the little things are fixed to get the very best price. we had a professional inspector come in prior to listing to let us know what would show up on a inspection that buyers always have done, then we knew in advance what to expect & took the time to fix it all. That way there wasnt a buyers price leverage against the sale price but this & that needed to be fixed.
Good luck