Oh I could go on and on about foundation and drainage. I'm in a walkout with ICF foundation. Its awesome and very well built. Only problem, the previous owner/builder royally messed up the footer drains. Put them 4 feet above footer, pointing into the air. Apparently water runs uphill in his universe. About 6 inches of crappy drainrock on top and then clay all the way to the top. Compounding this, he walled in the teleposts and main support beam in the basement so they can't be adjusted unless I almost entirely re-do the basement. This is all built on expansive clay soil. I dug a test hole on one corner and it was four feet of water before I hit the footer. We just had our second floor ceiling crack right across last week. Lots of movement from the telepost and partition walls in the basement pushing the house up as water infiltrates under the foundation and expands the soil. No water leakage though
So we are re-doing the entire footer drain system BY HAND. (Yes, all caps was appropriate). Every spare moment since June 1 and by the end of this weekend I'm almost half done. I've lost 13 pounds and my shirt sleeves barely button up on my shirts. Why by hand? Decks with structures, utilities etc in the way, at best a mini-ex could do the easy parts and save a couple of weeks. What with the economy and all, I'm probably just going to keep plugging away at it.
We are re-doing it quality, gravity drain to daylight, wrap weeping tile in membrane right beside base of footer, covered in gravel drain rock that also is wrapped in membrane all the way to 2 feet below grade, then a clay cap on top sloping away from foundation. Blueskin against ICF styrofoam and then delta drain dimple board on top of the blueskin. Nasty dangerous work (trench cave in danger) to have to re-do it. I'm already in 4k and figure it'll be about 10k when finished. Was quoted five times that to have it done by contractors in the area (rural).
So yeah, in hind-sight, I wouldn't buy anywhere on expansive clay soil unless I saw the footer drainage before it was covered up.
You are definitely wise to pause. Look for signs of movement in the house, if you see any, walk away fast! Basement floor cracks, garage floor cracks, uneven second floor floors, cracks in drywall, patches of cracks in drywall, stuck doors are all signs of foundation issues.
Also, shoot the whole house with a laser level, or make sure your home inspection does this. Be there when they do this too! If its off by more than a couple of inches (floor to laser line across entire level(s)) something isn't right with the foundation.