I know for myself and other investors they have had situations where someone in the building department says something verbally but then when you go to get the permits or approval things have changed.

Quote from @Sherry McQuage: Make sure to check the zoning to make sure mobile homes are permitted there; check for any hazardous waste designation for the area; will you need to have the parcels surveyed out in order to sell the size you intend? 

Also if this property is on septic that also can throw a wrench into the ability to call a space "a bedroom" as septic systems are sized and permitted based on the bedrooms.

Insurance- coverage for new engineering, permitting, etc8.  

Duplex have different zoning that may permit additional units.

I develop land in Nashville from finding the deals, getting all the entitlement and permits, financing it, to building it in house with my GC license.

Legal Implications & Ramifications : As an example; the iconic PCH homes in Malibu and many in the upper foothills might not permitted to build back, certainly not to the same extent or materials.

No lending institution or bank would be permitted to operate with those ratios.

Or, in most metro areas, you can obtain the list of permits that have been issued, and see who is receiving permits. 

Basically, "wholesaling" is no longer permitted.