Some friends recently had their entire home recarpeted by a reputable interior design company. They did a beautiful job -- everything except the kitchen, including 2 baths. About 4 days later one of the bathrooms developed a really bad odor problem. Really bad.
They called a plumber, who came out and pretty quickly determined it was a leaking-toilet smell. He pulled the toilet and found... the new carpet, laid over the wax seal (not determined whether it was the original seal or a new one), with a cross cut in it. Apparently they intended to cut out around the wax seal later, but Miller Time was coming on fast, or something, so they just re-set the toilet and vamoosed.
The carpet company owner was invited over to have a look, and the last I heard was properly humble and is making things right. The first thing he did was have the plumber pull the other bath's toilet to see if this was a mistake or SOP.
The plumber made out OK, and has a good story to tell.