my sister is thinking of buying a resale 3 rm flat. what is holding her back is the bathroom. it has cracks on the tiled walls and black seepage marks on the ceiling. Anyone has any idea if it is difficult to patch this up? Is it expensive?

The agent said that hdb officer will come and review the flat and get the owner to negotiate with the neighbour upstairs to patch up the ceiling.

But how can I ensure that they have done a good job and that the problem does not resurface?