The main thing with any kind of pavement treatment is to keep surface moisture from the soil beneath.If the paving is in good shape (i.e. no alligatoring or potholes) and looks like it's graded OK (no standing water after heavy rain), a seal coat can add life to the property.   

When trying to fix the septic system, I was halted by Baltimore County due to bad soil drainage.

You only filled with clean soil though right?

If he determines it can then you will need to speak with the building dept, also if not already, after hurricane sandy by me any structure undergoing a major renovations will need to be lifted and put on stilts, 

@Sandy Gabin yes I’m excited :)) can’t wait to clean it up and get it rented out .

Depending on what area of SC, our soil is very loamy (sandy) because we're on the coast.

Some of it depends on the area you live in, how deep the lines are, the types of lines (cast iron, clay, pvc, etc), and the soil types and such.For a job like that, you should get three quotes and have them try and break the quotes down by labor, parts, permits, and such.

And those with these type of houses, are often looking for suckers, to buy them, at too high a price, & be stuck with the constant threat of an house, which could collapse, at any time, due to sand is under such houses.

They more likely mean you need to know where you can and can't build, how deep your setbacks have to be, how much permits are going to be, does the city have funky ordinances that won't allow you to do what you want, what soil work do you have to do etc. 

I am a real estate closing attorney and work for Wessels & Gerber in Sandy Springs.