Like grace periods, free surveys, free legal work, concessions at closing, access to real estate agents at no cost?

No utilities on, no survey, purchase is as is and so on.  

I mean just to survey out the 20's is going to cost you a bunch.. ( if the county requires a survey.) and maybe there already is one..

Our realtor said that the property survey will definitively show two buildings on the lot which might help our case; but ultimately wouldn't prove that the CH wasn't built illegally. 

I would send out surveys to your buyers, using some sort of mailing list management via SurveyMonkey, AWeber, Mailchimp (or whatever you prefer). 

I've noticed that lots of wholesalers (not so much on Biggerpockets) have this tendency to ask questions like they are filling out a survey.

If the seller has an existing site survey and soils report, these should help give you more info on the dirt (and save you some $ if you were to subdivide and/or develop further).Let's connect offline if you think it'll help--happy to chat anytime.

Ask him for a survey or anything he knows about what is allowed on the land and what variances are required.  

The nerighboring property owners have crossed their survey lines right over my two relatives.

I like his books because for a PhD, he writes in a very easy to understand format and he uses surveys for his data.