Engineering and environmental impact study's and reports.

Crime Prevention Through Environmental Design.... read about it and adopt some of the strategies that will make the neighborhood more safe.Good luck!

Appraisals, Environmental assessments? 

Not going to go into details but I was privy to seeing 8 unit bldg. at a large apartment complex have to relocate 8 tenants to include them paying inconvenience restitution for not hiring a pro for a known environmental issue they new nothing about or how to handle it.

As for the apartment boom in southern California, owning an environmental consulting company gives me an advance look at what is coming.

Robert, you need to verify rents to actual net income, average rents don't tell us much.As in other areas, such small parks could be under environmental guns, shared wells, water supplies, sewage treatment, septics, etc.You should be able to get past utility bills for each pad which will show vacancies.What's the value of the conventional home?

Usually if a property is way overpriced, you will not get any regular showings, if you are getting them, means your price is probably pretty close so there would be some other factor possibly at play, if it is something house wise that can be rectified, do so, if something environmental ie..neighborhood, house next door etc, then usually a very slight drop shows potential buyers there is flexibility and may spark offers.

Aside from that, an environmental report, survey, and possibly a highest and best use report.

Phase I Environmental Report?

Good luck having a seller accept that in a hot market where another buyer will ignore it.If it really concerns you have a Phase 1 environmental survey done and ask the local environmental specialist what they would recommend.