Does the realtor own the piece of ground or are they just selling it for somebody?  If they are just selling it I would see if another realtor will sell it or if you can buy it direct from the owner and bypass the realtor if they are going to have that kind of attitude.

A few years ago there was a local farm for sale by a farm management company and they wouldn't sell it to anybody who wouldn't use their services on the farm so a area farmer went direct to the landowner and bought it behind the farm managers back which didn't make them happy but anytime you can make a farm manager unhappy you are doing something right.