Checking posts and footings is smart but that is not the thing that would have saved this guy money. Even if his posts were solid, the frame was already toast. Rotted joists do not show up until you start pulling boards, and no amount of pre-checking tells you what is hiding under there. I have been down this exact road and the real lesson is to set a hard cap before you buy anything. Something like if I find rot in more than a couple joists, it all comes down. The $400 hurts but the two weekends are the part you never get back. Patching a deck with a dead frame is just paying twice for the same tear down.

That blank space thing drives me nuts too. My family has a map from the 1770s of upstate New York where our whole valley is empty but some tiny creek twelve miles off got its own label, and I spent way too long trying to figure out why. From what I've read, the mapmakers were mostly fur traders and priests, so they only wrote down water and Native trails since that's what they actually used, and everything else was just filler to them.