honestly I would say the MOST common is water heaters not having pop off value vented to outside of the crawl space.  Code changed on that a few years ago and all my sellers get dinged for it

Dirty air filters are never a big surprise. The big surprise is why they  were not changed!

Tammy Lankford, nailed this one...

Problems with cedar shake roofs.

Termites would probably be #1, after that retrofit issues.

Fred Griffin the problems depend on the age of the home. Older homes do have 'old' technology/systems for almost everything - and as per the code then.

I remember one of the years where almost every other home showed mold! Not as much now, though.

In my area it's usually a moisture problem that is caused by a current or past plumbing leak. My latest inspection turned up some electrical issues that aren't up to code. 

Home inspectors are almost always saying the HVAC units need to be checked out and serviced. They also talk about not enough dirt around the foundations. Mold is not a big issue.

HVAC and wood destroying insects!

Simple stuff Fred. Old CO and smoke detectors and the lack of GFCI outlets.

I would say wiring or gas venting over a water heater.

Termite. Dryrot. Old electrical. 

Basement issues, and antique bricks that need repointing.

wet basements

Most often is ungrounded outlets. I see some leaky faucets and rarely most except for the REO homes that saw frozen pipes over the winter

Bad Furances

It is diverse and meaningful for the most part. What I object is opinions on what will happen and what should be fixed. Just report the condition thank U

I  see roofs (cracked tile) as very common, and also the age of mechanicals (a/c, water heater), and last but not least, alot of deferred maintenance.  The homes are no older than 30 years, but so are some of the mechanicals Fred Griffin! 

Hi Fred - I don't think we have good habits in HVAC filter changing - dirty furnaces are a very common finding.

I'm seeing picky stuff like electrical outlets outside not being covered.  Stuff that was never an issue until this year.  I also see some inspectors who don't know how to use shower controls that aren't "standard" and falsly report them as broken.

Most home inspectors are not certified to call a black spot mold. At best, they should make note of the black spot and recommend testing for mold from someone certified to test for mold. You can not visually determine the presence of mold because it looks just like mildew.

I had one licensed home inspector claim the black tree lichen on some structural supports was deadly black mold. Testing showed no presence of mold.

Some wood rot on the facia is an almost certainty in most inspections.

Just an astonishing amount of deferred maintenance.  I don't understand it, but it seems to have gotten worse over the past few years.  So many people don't care of anything. 

Moisture and mold, definitely.

A/C life expectancy is the biggest issue.

I just had 2 inspections with major structural damage!

Seems to be wood rot.  I guess it is just the moisture in this climate!

I don't track this type of metric.

It depends on the property.   HVAC.  Plumbing.  Electrical.  Roof.  Foundation. Termites.   

There is no perfect property.   

Roofs and HVAC seem to come up frequently. It's amazing how many agents try to claim that a roof with cracked and curling shingles was just replaced  4-5 years ago.

leaks, loose toilets, termites, HVAC issues

The toilet is not secured to the floor.

Roofs and HVAC

mold is common in attics and basements.... lack of ventilation.....

GFI's not working, double taps in electrical boxes.