Things I've Seen

Some of the common, and some of the most unusual problems encountered.
Roof:  Instances of bare or missing shingles where water has entered the attic, or rot where the sheathing has become too soft to support much weight, and loose flashing allowing daylight into the attic from outside.  Leaking skylights and squirrel and raccoon damage to soffit and trim is not unusual.
Attic:  Mold and mildew on interior structure and sheathing, possibly due to poor ventilation, clogged vents or bathroom exhaust fans vented into the attic are frequently seen.
Electrical:  An 80 year-old widow’s husband had a welding hobby and blew fuses when using his equipment.  Rather than replacing the fuses, he used thick-walled copper pipe sections in place of fuses on the main fuse holders on 200-amp service.  I’ve found many unsafe multiple tapping, burned circuits, arching switches and even an electrical box mounted on the inside of a shower wall!
Plumbing:  In one home, the crawlspace drain piping was in such poor condition that for some time, when the toilets were flushed, a portion of the waste was escaping the pipes and being deposited into the crawl space.  Other not so uncommon problems include unsealed sanitary sumps where a basement bathroom is involved, “creative” piping around obstructions which restricts proper drainage, and the ever-popular drain piping which runs uphill!
Foundation:  At one particular inspection, a foundation wall separated from the rest of the foundation.  It tilted outward so much that at the top you could see a few inches of daylight from the crawlspace.  The siding and back wall were tilted outward from the sill plate.  Another home had settled so much it had wedges everywhere to level out such things as doors, cabinets and floors.  Unfortunately both tubs had their drains at the “high end” of the tub causing approximately 1½” of standing water at the “low end” of the tub.
Furnace:  Another home’s furnace had a large visible hole in the heat exchanger – as big as your fist!  In has been our experience that many furnaces are in such poor operating condition that the level of carbon monoxide out the flue, in the case of a backdraft, could have been dangerous, or even deadly, to the occupants.