An electrical system is so detailed, there are too many items to discuss, but I will mention several.
1. Bonding of metallic water, gas and fireplace chimney pipe systems and grounding of appliances and devices are an important safety requirement. Pipe bonding is made using bonding jumpers that should be accessible, so this can be visually inspected. Grounding of appliances and devices can be inspected by electrical test equipment. Grounding starts with the service-equipment grounding electrode, which many times are incorrectly installed.
2. Extension cords are a temporary, not a permanent wiring installation. However, many times I observe homeowners that performed their electrical installation with the use of an extension cord, which is incorrect.
3. Another incorrect homeowner installation is installing electrical cables and conductors in an attic or garage where conductors are not installed in protective conduit and conductor splices are not installed in approved boxes with covers.
4. Homeowners are not always at fault for incorrect installations. I observe incorrect installation by licensed electricians of a sub panelboard or panelboard in a secondary building many times. Quite often the incorrect installation involves the grounding and/or grounded (neutral) system.
5. I hope most inspectors know where ground fault current interrupter (gfci) protection is required, and this is probably as detailed as many inspectors are with an electrical inspection. Simply, gfci protection is for personnel protection to de-energize a circuit within an established period when a current to ground exceeds the value of the device. The device will open before an individual being shocked, or worse, electrocuted.