Section 18, 24S, 34E, eddy county

New here so please excuse ignorance! My mom owns 7.5 NMA. An offer has been made and she would like to sell. How can I best understand fair market value? My assumption is that someone will but this from her and will turn around and make $$$$$ but she’s fielded offers for years and is now inclined to sell. Any thoughts or resources for more info much appreciated. I don’t know if it’s appropriate to quote the offer price or firm here so I’ll hold off for now.