If there is a chance that will purchase a house or an office older than 25 years, it would be better to check if the wiring is up to date. This will help you get rid of problems with wiring occurring in the future and will help to better estimate the costs of the building. If the property is more than 25-30 years old, than the wiring system should probably be replaced at least partially to bring it up to current standards. If you see that there is a mix of different socket and switch styles, this means that the property was partially rewired already. If there are old-fashioned-style fuse boxes, with big white ceramic-style fuses, then you will probably need a complete rewiring for your safety.