Check the pipes! About 18 months after moving in we had to replace all of the pipes under the house, which wasn't cheap. While we did a building inspection that covered the structure of the house, we missed the plumbing.
Also, another nasty surprise and one that is fairly common - asbestos. It's amazing where you find this stuff, again another costly oversight.
We had a similiar experience to Darren when we moved into our place. The water was rust coloured. I wish I'd tried the taps!
And it reminds me that I must post about our current plumbing issue...
I would have liked to have known about how dirty the oven and rangehood was.
Building inspection came back with roof tiles had slipped in some part and just needed to be realigned. Partner got up on the roof to clean the gutters a week after we moved in to find out the whole roof needs to be re-pointed as the morter was crumbling. After several quotes from roof sepecialists, consensus was they put the morter in with a paint brush and over time just fallen apart.
Who would have thought roof specilists in Melbourne are all booked out until May to complete the job!
Check to make sure the taps in the shower have been sealed! The shower in our ensuite hadn't been sealed properly and the water was dripping down the back of the taps and into the wall. We had to rip the plaster off the other side of the wall and rebuild the door frame right next to it. If I'd known what to look for at first it would've saved a huge amount of trouble.
I'm a bit like Darren. I wish I knew how much plumbing work would be needed to be done at our place.