Structure that is not protected from damage (like a roof), will also have an average life expectancy.Survey what you have and replace all the systems due to fail in the next 5 years.  

Been at this a couple of years...talked With a number of sellers...they all seem to think I'm nuts when I get to the part about my offer being 60-65 cents on the dollar...is this realistic?

I think they're still operating only in California(correct me if I'm wrong) and haven't read much other than forum comments or a post from this OC broker http://malakaisparks.com/why-haus-will-fail/.The sites traffic doesn't seem to be growing much so who thinks this is still going somewhere?

And if you fail get retested.

They are an elderly couple whom have resident status in another state and are looking to sell due to the failing health of the husband.

Failed bids are waste of their time and yours.

Just as if the landlord fails to make repairs, you can serve them with a 30 day notice to "QUIT" or make repairs.

The brokerage can give you the tools but it is not a magic wand to make the money roll in.90% of new agents fail the first year and leave the business.  

Here is an excellent example of a failed city council and local politicians in the name of helping the poor!!! 

Some of that could be because the seller simply failed to disclose certain operating costs.