Appraisal for Industrial use land?

[Jorge Leon]

Hello everyone. 

My family has a 60 acre plot of farm land near a major city, the area has been booming with industrial/warehouse construction for the last 10 years, we are next up in the corridor and have decided to sell. Someone offered us 6.3 million 2 years ago, the deal fell through. We are now in a marketing agreement with an experienced well know name in the area, he has received offers for 6.75 million but says we can end up with 7 million (after counter offer). My father says he wants 8 million (with no real justification other than some questionable comps). Can we have an appraisal done for this type of land? How do we know our broker is not in cahoots with the buyer and/or underselling our land. How can we get a realistic valuation? Any advice welcome.