Need help evaluating a purchase offer in Miami

[Olga Levin]

Hoping to get some advice on valuing a commercial/indurstrial property and an offer that was received.

A friend owns a lot in Miami 33147 area. He operates a car repair and sales business there. He received an offer from a developer to purchase the property with 90 day inspection period and another 240 day for permits + 3 30 day extensions.

The offer came through a guy who came by the property to see if they wanted to sell and then brought a buyer a few weeks later. It's not currently listed on the market. The buyer is a big developer that intends to convert the lot into a gas station.

I am trying to figure out if the terms of waiting for the permits to come through are standard or if the buyer is trying to put the risk on the seller while tying up the property? 

How can I evaluate if the price offered is close to property value? Hard to find comps in the area, since it's a big lot with some structures and a small office, but I am guessing most of the value is in the land itself. Can someone recommend a local broker who knows the area and can give some ideas?

Does it make sense to list with a broker to get the best offer if he ends up wanting to sell?