Occasionally at a home inspection I find that some walls are not visible, and because my Clients usually expect me to have X-ray vision, I have to tell them that, uh, I don't. So I warn them that there could be some damage behind whatever is obscuring the wall from sight.
This first picture was in the very large home gym room in a property owned by a professional football player:

I had never seen such a great collection of beer cans in all my life. I jokingly warned my Clients that perhaps visitors to the gym who did not meet their weightlifting goal for the day got to take out their frustration on the wall, and when the damage got so bad, they simply started stacking beer cans against the wall. Well, I got a call from my Clients while they were at the final walk-through telling me that my joke was not so funny because that's exactly what had happened. Behind this wall of beer cans was a wall full of holes. Escrow got delayed for a week while the Seller and Buyer argued over who had caused the damage and who was going to repair it.
The following picture shows a collection of Hot Wheels, still in their original packaging and proudly displayed on the wall. In this property, there was a huge moisture stain on the wall resulting from a leak in the plumbing upstairs.

And lastly, in the following picture, there were some cracks in the lathe-and-plaster wall which needed to be looked at in more detail to determine what had caused them and whether or not the cause was active or inactive.

Moral of this blog: As much as I (and most home inspectors) would like to be able to see all and be all, it's just not possible. So listen to your home inspector when he warns you about areas that are not visible or not accessible and make sure you look at those areas during your final walk-through. Remember to take a copy of your home inspection report with you as a friendly reminder. You want to make sure that you're 100% happy with the property and that all the potential headaches are either taken care of or headaches that you can accept.
It's amazing what some sellers will do to hide issues.