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 buy 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.