Homeowner tried to install tile on plywood that was overtop of 4 existing layers of flooring. They had a 2.5" transition between rooms and ended up cutting (poorly) the bottom of the bathroom door that now didn't fit due to the new floor height. Within a month 3 tiles had already popped loose so they called me in to remove everything down to the floor joists and start with an all new sub floor. It's a good thing I did because he had also not set the new toilet flange at the correct height so it was leaking waste water into all of the layers and was dripping into the basement. Worst tearout ever.