But underneath the piles of dirty clothes and empty beer cans, we have not found much deliberate damage.

I would definiltey get a soil test. 

The biggest selling point was to rip up the old stinky carpets and refinish the gorgeous oak floors underneath.

The soil is very easy to dig up in this location. 

For example, you can have a business card with your name, and a tagline underneath it, "I work exclusively with investors!"

I am trying to figure out a better way to avoid putting up a yard post every time a property is available for rent and remove it every time a vacancy is filled.For single family homes, I think I will rig together a post where the mail box can be mounted on top of it, and I can simply add a hanging sign underneath when I have vacancy.For multifamily the mail boxes are on the wall or doors, so I don't have anything in the yard that I can mount to.  

There is all manner of ways to get hurt building.. soil issues, un knowns that you don't know until you start..

I know a lot of people in pier and beam houses that have constantly shifting foundations (North Texas soils are pretty unstable) and have lived with it for decades. 

Asbestos floor tile is not.Asbestos-containing ceiling tiles, floor tiles, undamaged laboratory cabinet tops, shingles, fire doors, siding shingles, etc. will not release asbestos fibers unless they are disturbed or damaged in some way.Asbestos pipe and boiler insulation does not present a hazard unless the protective canvas covering is cut or damaged in such a way that the asbestos underneath is actually exposed to the air.

Very reasonable if they supply the soil test report.