It always leaves signs...usually a white mineral trace if it has been ongoing but presently dry, or more obvious wood rot, staining, or mold.

You can even stain it to add color and hide flaws.

It has cosmetic issues that don't look alarming (Paint scratches and stained carpet).

Even if your resident did something, like stain the carpet, if you manage the insurance process correctly, insurance will buy you a new carpet anyway.

Even removes nicotine stains from walls.

The process the property management company uses is to flip the carpet over and black light the underneath for urine stains.

Pick up poopy toilet paper on the carpet .kill rats by stomping on them ,remove thousands of squirming maggots out of appliances .clean up crusty blood stains .mow yards with grass two feet high with a weed eater .. 

We added a screened in back porch and stained both decks.

An eviction is a serious stain on a tenant's record.

I learned that some of the stains are just not coming out and they give the floor character.