Clumping kitty litter flushed down all the toilets…turns into concrete down in the drain.
Appliance cords pulled out of disposals, etc.
bearing grease smeared on walls, doors , etc.
Fireplace flue pipes removed inside the attic.
Large objects places in odd places to hide defects; once had a speed boat pushed up against the wall and into the corner of garage. Found water leaks inside the walls from upstairs HVAC unit. There was no insulation on the suction line so it sweat like a whore in church and ran down inside the walls (mold, stains, wet drywall.
My all time favorite one was a vacant house with a single bed pushed up against a wall under a window in one bedroom. It happened to be pouring down rain in a major Tropical storm passing thru. I moved the bed and water was leaking down from the overhead suspended ceiling and running down on the inside of the window. Popped a ceiling panel and found a wad of roofing tar the size of cat had been poured (and had fallen out due to the shear weight of it) into a rotted out section of the roof directly above the outside wall. The real kicker was when I opened the house up there was a paper sign taped to a kitchen cabinet that had a handwritten message on it…“The roof does NOT leak”. Nothing like telegraphing that there was a problem.
If it looks out of place or suspect…go the extra mile and double check it. It most likely is. Freshly painted wood always got my attention especially soffits.