What to look for when buying an oldish apartment room?

Hey,

So my wife and I are looking to buy in Tokyo and we've across some listings that seem cheaper than usual. We're looking for something under 10 years old but even than usual lower prices kind of scare us.

We're planning to look at a few places this week and I'm wondering what exactly do we need to watch out for when checking an apartment out.

For example, what are some red flags to look out for or what things do people tend to hide when selling a place.

Thanks for the help!