A note to just to add:
A local unit of government such as a building enforcement official can not require a building to be brought up to todays standards in most cases as to Constitution of the United States, and most states Constitution, protect us from these requirements.
With that said, we also must know that a company offering a service is not under this same obligation such as insurance and loan companies, they can refuse service if a building doesn't meet their minimum safety standards, so in Home Inspection it will be these requirements by these companies that should guide us, as well as looking for things that are unsafe and or didn't meet code at the time of the permitted work.
You will need to get these standards for FHA, VA, HUD and others, so you will have the info as to what you will be looking for.
Here is a small list of some of their requirements:
100 amp service minimum
No fuses in service panel
GFCI protected receptacles:
In kitchen within 6' of sink
Bathrooms
Garages accessible only, dedicated (freezer, refrigerator, garage door opener exempt)
Outside
Pools
No open splices, or other unsafe wiring.
Proper bonding and wiring of service's
proper grounding electrodes installed.
no more then one neutral wire per terminal (grounds can be if per panel label)
many breakers only allow one wire, but you must learn that some do allow two, such as Square D both QO and Home Line, you must look for the info on the breaker.
And always remember, you are only providing a "informational only" inspection, here we had some HI's who thought they carried the same weight as a building official, you don't, a building official is in fact an officer of law. our state went after them for posing as an officer of law, to get them to stop, now we have a state wide HI licenses and much of these problems went away.
There are also many sites out there that cater to HI's but remember to research what you are told, there are a lot of myths out there, and some of these come from these HI's sites.