Patent vs. latent defects
There are two kinds of defects. A patent defect is clearly visible on inspection of the property, such as broken window or cracks in the wall. All patent defects should be listed in the offer to purchase, along with who is responsible for fixing them.
The other type of defect is a latent defect, which is not easily picked up by a superficial inspection. Examples of latent defects include a leaking roof or faulty geyser.
Claiming a portion of the purchase price
It will be dependent on the circumstances, but if a latent defect is found, the buyer will be able to cancel the contract or claim a portion of the purchase price.