Any odd dark stains under windows, even at floor level, could be a sign; as could deteriorating sheetrock around or under the windows.

There's always little things like stained linens or broken dishware you'll need it for.

My renters absolutely destroyed beyond regular wear and tear (playdoh ground into carpet and dog stains and rips) the carpet that I had installed in the unit just before they moved in.

It has a neat atmosphere... stain glass windows, etc.

It's quite a bit cheaper and if a guest stains a pillow all you have to do is buy another cover. 

You need some heavy duty stuff to get hard water stains off of an all-glass shower door.

If it is visible damage in the middle of the floor and deep you may need a professional repair otherwise you might just be able to touch up with stain and charge them for supplies. 

Assuming I provide stains and polyLay floating and/or sheet vinyl on level floor - How much per sq ft?

There are chemicals that you can spray on them to eliminate this or replace the stained subfloor plywood.

They are claiming that we must have the carpets professionally cleaned before move out or else they will charge us for it.Keep in mind, this is a short term lease, we have only been here for 7 months and again, there is not a single stain, or any damage at all.