The pic below is after I tore up the top layer and did a quick wash with bleach and water on the bottom.

It's helped pay for, without a deductible on my primary insurance: -A new King Bed after guests broke the other bed when they showed up and most likely jumped on it-A new Queen Bed  and Box Spring after similar situation in the upstairs bedroom-A new Dining Table after guests left a bunch of super hot pots/pans on it and bleached the wood-Repaired door frame after a guest must have broken the front door-A new sleeper sofa after guests bent the pull out metal hinge to the point where it would no longer retract into the sofa. 

If you have black marks from rusted nails, which adds character, youre SOL unless you bleach the floor which doesnt really help.

We have had to do substantial gutting of the property, spray every surface with bleach, and leave the windows opened for months to remove the smell.  

I would also recommend getting white towels and sheets so you can bleach them.

Outbuildings didn't have to be touched beyond basic clean out.I agree with others who have stated that plumbing and electrical can get you, but it's so worth working with a jack of all trades general contractor who knows her/his stuff and you know codes so you can give very specific direction and have them get the job done without having to use a full-fledged plumber.The following has nothing to do with your question about biggest expenses, but may save you big dollars in the long run:We were given some tips that have paid off: vacuum out your HVAC system to the best of your ability prior to inspection (inspectors see dirt or dust and they give you poor marks and tell potential buyers that a professional needs to be brought in to clean out the system); run Draino through your tub/shower drains (if you're leaving existing tub/shower in tact) prior to listing and test the drains to make sure there is good flow (we might or might not have used the tubs to clean paintbrushes, which resulted in REALLY slow drains); If you have a hand dug or shallow well, run bleach through it (lots of instructions online as to how to get bacteria out of the system when a hand dug well is involved) and flush the bleach immediately prior to inspection.I hope some of this helps. 

Bleach and a pump up sprayer.

I'm going to go wash up with bleach now.

Both times I suggested they clean toilet inside and out, and clean floor around it with a cleaner w/ bleach.

Using bleach and ozone machines from Amazon you would have no idea the absolute hellish filth that once existed there.