Painting over unresolved moisture issues, in particular, is a significant and common mistake. If a wall has water damage from a previous leak, painting over it without addressing the underlying cause will almost certainly result in the stain bleeding through again, along with continued risk of mould growth. Reputable Painters in Sydney will flag these issues during their initial asses... https://logcla.com/blogs/1972750/Sydney-Property-Painting-Common-Mistakes-Homeowners-Should-Avoid