They provided us with an estimate for septic system repairs done by a reputable company; however, when we had our usual company come out to do the repairs they found that the soil was not suitable and they would have to reach out to the county to run (perc) tests and to give the "okay" to continue work.

Unless you perform a Phase 1 to make sure the soil is clear, this can potentially be an issue.

If the soil is at a capacity and no longer perking then there is enough of a lawn to move the distribution system and dig some newlegs.

I have removed the sheetrock underneath, but have no shower pan experience.

In a lot of ways the brokerage model of agents being underneath a broker is outdated. 

Many of these folks are professional engineers - soils, geologic, structural, MEP, civil, utility. 

But if attorney review is still open you can back out for any reason (as unethical and soiling to your reputation as doing so may be), assuming you are using a CAR or the Multiboard contract.The bigger question is how in the world is this square footage issue possibly a surprise at this point?

“S trap plumbing throughout the home underneath sinks.

If your someplace that has harsh winters, frozen pipes can be a nightmare for mobile homes so I would suggest checking the insulation underneath etc...I think the main difference is that mobile homes tend not to be as durable as a normal sf stick built home so your ongoing maintenance and repairs are usually higher.

Subsequent scoping of the main line (and multitudinous other testing) revealed 17 feet of standing water in the main sewer line underneath my property extending under the adjoining property.