Aside from the general information about the property you are considering purchasing, such as the price of the property and whether or not the land is owned by the owner, you should also be especially careful to check if there are any restrictions or details that are not legal.
In general, property prices that are much lower than the market price are often for properties where land ownership is unobtainable, or for non-reconstructable properties that do not meet the provisions of the Building Standards Law regarding the obligation of access roads.
Also, please note that most of the yields listed in property descriptions are "surface yield," which are based on the rental income before subtracting the property's management fees and other expenses. Please do not misunderstand the surface yield as the real yield.